Method implemented in a user equipment UE for use in a wireless system

ABSTRACT

In some implementations, a method implemented in a user equipment UE for use in a wireless system for single carrier frequency division multiple access SC-FDMA, the method including receiving an assignment of a scheduling request resource in the wireless system comprising a plurality of subcarriers. A user ID is encoded. An uplink control channel signal comprising the encoded user ID is transmitted on the plurality of subcarriers of the assigned scheduling request resource.

CLAIM OF PRIORITY

This application claims priority under 35 USC §119(e) to U.S. PatentApplication Ser. No. 61/579,964, filed on Dec. 23, 2011, the entirecontents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to a method of sending and receiving schedulingrequests within wireless communication systems.

BACKGROUND TO THE INVENTION

One of the challenges of wireless communications is that there is afinite amount of bandwidth available over the air, but an everincreasing population of mobile devices trying to access it. Throughscheduling requests, devices are able to share radio resources and, whenthey require access to these resources, can be granted access to usethem. Many wireless communication systems implement some form ofscheduling requests, however it is emerging that these current solutionsare unable to cope with the changing behaviour and requirements ofmodern mobile devices.

Long Term Evolution (LTE), a standard for high-speed wirelesscommunication, comprises an Evolved UMTS Terrestrial Radio AccessNetwork (E-UTRAN) coupled to an Evolved Packet Core (EPC) Network. InFIG. 1 the E-UTRAN 103 comprises one node type eNB 102 whilst the EPC104 comprises 3 node types. Whilst the term eNB is used to denote theaccess node used for the Uu interface (interface that links the UE tothe E-UTRAN), there are a variety of access nodes capable of operatingon the Uu interface, such as relays, home eNode Bs, etc. Therefore, forthe purposes of describing the embodiments herein, the term eNB may beused to refer to either the eNB, or to other access nodes performingequivalent or similar operations on the Uu interface. The ServingGateway (SGW) 105 routes user-plane data within the core network, theMobility Management Endpoint (MME) 106 handles mobility and connectioncontrol between the UE and the core network, and the Packet Gateway(PGW) 107 ingress/egress node routes data between the core network andexternal networks. FIG. 1 also shows the network interfaces betweennodes

The LTE system has 3 main uplink physical channel types: Physical RandomAccess Channel (PRACH), Physical Uplink Control Channel (PUCCH) andPhysical Uplink Shared Channel (PUSCH),

The Physical Random Access Channel (PRACH) is a contention-based channelwhere transmissions from multiple users need only be very looselysynchronised (time of arrival differences may be of the order of 0.1 sor more). Devices using PRACH normally communicate on an ad-hoc basis.

PUCCH and PUSCH orthogonal resources, on the other hand, require tightersynchronicity of devices (time of arrival difference of order of 5 μs orless within the cyclic prefix duration of a Single Carrier FrequencyDivision Multiple Access ‘SC-FDMA’ symbol) and therefore allow formultiple devices to use shared resources within the uplink systembandwidth.

SC-FDMA

SC-FDMA is the modulation scheme used in the uplink of LTE. The schemehas some similarities to Orthogonal Frequency Division Multiple Access(OFDMA) but also some key differences. In both OFDMA and SC-FDMA, thephysical resource is sub-divided into a time-frequency grid of ResourceElements (REs), each RE consisting of one unit of frequency (onesub-carrier) and one unit of time (an OFDMA or SC-FDMA symbol duration).The OFDMA or SC-FDMA symbols are both pre-pended with a cyclic prefix(CP) (an end portion of the symbol is copied and inserted at the startof the transmitted symbol).

In both SC-FDMA and OFDMA, information bits to be transmitted mayundergo steps of encoding (to form encoded bits) and the encoded bitsare usually then mapped to data modulation symbols (for example, usingQPSK, 16-QAM or 64-QAM modulation schemes). A key difference betweenOFDMA and SC-FDMA concerns how these data modulation symbols are mappedonto the time-frequency resources.

In the case of OFDMA, there is usually a one-to-one mapping of datamodulation symbols onto sub-carriers. That is, N modulation symbols tobe transmitted within one OFDMA symbol duration are each mapped to acorresponding one of a set of N sub-carriers.

Conversely, in the case of SC-FDMA, there is usually a one-to-manymapping of data modulation symbols to sub-carriers. That is, one datamodulation symbol is mapped via a spreading operation to a set of(usually complex) numerical values, and each of these numerical valuesis then used to modulate a particular one of the N sub-carriers.Furthermore, other data modulation symbols may be mapped via a similar(and usually co-ordinated) spreading operation to the same set of(usually consecutive) N sub-carriers.

The spreading operations are usually co-ordinated in order to ensurethat the multiple data modulation symbols remain orthogonal to oneanother. Therefore, the data modulation symbols may be transmitted frommultiple devices and received with simple linear operations with lowinter-device interference. This behaviour can increase spectralefficiency by allowing multiple devices with small amounts ofinformation to transmit to share a set of subcarriers.

When multiple modulation symbols in one device are spread over the sameset of subcarriers, each modulation symbol creates an additional set ofN numerical values, and these are linearly combined (across thecombinations from each of the contributing modulation symbols) to formthe eventual numerical values that are used to modulate eachsub-carrier. This linear combination of spread symbols can be viewed asa transform operation. The transform operation is usually designed toensure that the resultant transmitted signal has a lower Peak-to-AveragePower Ratio (PAPR) than its OFDMA counterpart. The transform operationmay comprise a Discrete Fourier Transform (DFT) as is often used in thecase of uplink transmissions for LTE, but other transforms are alsopossible that preserve a low PAPR of the transmitted signal. Similarly,when only one modulation symbol (e.g. either a data modulation symbol ora reference symbol) is transmitted over a set of sub-carriers, thespreading sequence is also designed to minimize its PAPR. In this case,spreading sequences with constant (or near constant) amplitude and zero(or low) autocorrelation (“CAZAC”) properties are often used such aswhen constructing uplink reference signals or uplink physical controlchannel transmissions in LTE.

Thus, a data modulation symbol is transmitted over a set of Nsub-carriers for SC-FDMA, whereas one data modulation symbol istransmitted over one sub-carrier in the case of OFDMA.

PUCCH and PUSCH

FIG. 2 shows an example structure of a sub-frame 210 spanning 1 ms inthe time dimension and an uplink system bandwidth in the frequencydimension. The sub-frame comprises two slots of duration 0.5 ms each.The sub-frame 210 can be pictured as a collection of discrete blocks220, each comprising 12 sub-carriers of 15 kHz each in the frequencydomain and a single SC-FDMA symbol 260 in time. In this example, eachresource block 250 (of PUSCH or PUCCH resource) comprises 12×14 resourceelements (RE) within a sub-frame, where a RE is one sub-carrier unit offrequency and one SC-FDMA symbol 260 of time resource. The number ofSC-FDMA symbols 260 per sub-frame may vary depending upon systemconfiguration, thereby also affecting the number of REs per sub-frame.The system configuration may be a function of a cyclic prefix (CP)duration of the SC-FDMA symbols. The PUSCH resource 240 is located inthe central frequency region with the PUCCH control regions 230 at theedges above and below. Within a resource block 250, certain SC-FDMAsymbols may be used for reference signal (RS) purposes. Referencesignals are signals known to the receiver and which may be used forestimation of the radio channel in order to improve demodulation anddetection performance. In the example of FIG. 2, the 4^(th) SC-FDMAsymbol of each slot is used for PUSCH RS. The symbol locations of RS forthe PUCCH region may vary as a function of a PUCCH signal format. Forexample, for a PUCCH format 1 signal, the RS may be located on the3^(rd), 4^(th) and 5^(th) SC-FDMA symbols of each slot, whereas for aPUCCH format 2 or PUCCH format 3 signal, the RS may be located on the2^(nd) and 6^(th) SC-FDMA symbols of each slot.

Synchronised mobile devices know the time and frequency locations ofthese resources, hence the PUSCH resources 240 can be dynamically sharedunder the control of a scheduler (allocated using uplink grants withinDownlink Control Information (DCI) messages sent on the PhysicalDownlink Control Channel (PDCCH). Generally it is within this PUSCH 240resource that uplink user data is transmitted in the sub-frame 210.

The PUSCH 240 is the only physical channel to which the UL shared(transport) Channel (UL-SCH) may be mapped. Therefore when a user hasdata to transmit and uses the transport channel UL-SCH, it must firstgain access to the PUSCH 240 and to do so must inform the scheduler atthe base station (eNB) 102 of this need.

A PUSCH transmission may carry an Uplink Shared Channel (UL-SCH)transport block which may include user plane data, control information(like MAC headers) and RRC signalling. FIG. 3 shows the construction ofan UL-SCH MAC transport block 300, made up of a MAC header portion 310and a MAC Payload portion 320 which itself may comprise MAC controlelements 330, MAC service data units (SDUs) 340 and MAC padding bits 350

The shared PUSCH resource 240 is available (under control by thescheduler) for all commonly connected devices to use for thetransmission of data. The UEs may indicate to the eNB their need toaccess the shared PUSCH resource 240 by one of several methods,including i) executing a random access procedure on a Physical RandomAccess Channel (PRACH), ii) transmitting a Buffer Status Report (BSR) ona PUSCH resource previously allocated via dynamic scheduling to the UE,or transmitting a Dedicated Scheduling Request (DSR) on a PUCCH resource230. The eNB may use such indications when determining its allocation ofthe PUSCH resources 240.

The PUCCH resource 230 is semi-statically configured for reportingchannel quality or channel status indicators (like CQI/PMI/RI), and fordedicated scheduling requests (DSR) to aid the eNB in its allocation ofPUSCH resources 240. Portions of the PUCCH resource 230 are dynamicallyallocated for reporting ACK/NACK information. To achieve the dynamicallocation of PUCCH for ACK/NACK, the PUCCH resource used for aparticular ACK/NACK transmission may be associated with the location ofa corresponding DCI message on PDCCH.

The current LTE system is designed around the premise that connectedmode is used only for UEs 101 with recent data activity. Therefore, acommon assumption is that on entering RRC connected mode, a user will besemi-statically assigned (usually for the duration of the connected modestay) dedicated SR resources on PUCCH for the purposes of informing theeNB 102 of the UEs 101 need to transmit data on PUSCH, subsequent to anew arrival of data and having previously had an empty transmissionbuffer.

Therefore, in the current “dedicated SR” approach for connected modeusers, each user is assigned its own reserved time/frequency/coderesource on uplink, on which the UE 101 may send a signal to indicateits need to access the PUSCH.

PUCCH Format 1

The signal commonly takes the form of PUCCH format 1, illustrated inFIG. 4, which is formed using a combination of frequency domainspreading 410 and time domain spreading 420 of a single-valuedmodulation symbol d(0) (d(0) is set to the value “1”). The single-valuedmodulation symbol d(0) is spread in both the time and frequency domainssuch that it occupies all of the REs within the sub-frame and resourceblock on those SC-FDMA symbols that are not used for RS 430.

The presence of PUCCH format 1 on the UEs dedicated PUCCH resource issufficient to indicate to the eNB that a UE needs to access PUSCH. Theabsence of PUCCH format 1 is interpreted by the eNB as “no current needto access PUSCH”. Thus, PUCCH format 1 uses “on/off keying” to conveyits information. Reference symbols 430 are inserted in the 3rd, 4th and5th symbol locations of each slot (for a system employing normal cyclicprefix length).

There are also two additional variants of PUCCH format 1 that aredefined within the standard, known as PUCCH format 1a and PUCCH format1b. These have the same signal construction to that of PUCCH format 1described above but allow for BPSK and QPSK modulation (respectively) ofthe symbol d(0). In this way, PUCCH format 1a may carry 1 bit ofinformation (BPSK) and PUCCH format 1b may carry 2 bits of information(QPSK). These variants of PUCCH format 1 are used for transmission ofHybrid Automatic Repeat Request (HARQ) feedback, also known as ACK/NACKinformation.

PUCCH Formats 2 and 3

There are other PUCCH formats in the existing LTE specification, notused for DSR. PUCCH format 2 is used to carry Channel Quality Indicators(CQI), Precoding Matrix Indicators (PMI) and Rank Indicators (RI) forchannel feedback purposes. PUCCH format 3 is also available forproviding HARQ feedback (ACK/NACK) for PDSCH transmissions. Both ofthese formats can carry more data than PUCCH format 1.

DSR resources for different UEs may be multiplexed within the PUCCHresource in the time, frequency or code domains. Time multiplexing isachieved by assigning a sub-frame periodicity to each UE and assigningdifferent sub-frame offsets to those UEs such that DSR transmissionsoccur at mutually exclusive times. Frequency multiplexing is achieved byassigning different resource blocks to different UEs such that DSRtransmissions occur in mutually exclusive frequency regions. Codemultiplexing is achieved by assigning different time and/orfrequency-domain spreading sequences to different UEs such that DSRtransmissions occur on different code resources which are separable bythe eNB receiver. Combinations of time multiplexing, frequencymultiplexing and code multiplexing may be used. A problem with the DSRscheme in PUCCH format 1 is that it does not scale well as theconnected-mode user population is increased. As the connected modepopulation size increases, either the amount of total system ULresources that are needed (to reserve mutually exclusive PUCCH resourcesfor each of the UEs) becomes excessive, or if the total DSR resourcesare constrained, the SR latency performance is then degraded (i.e. SRopportunities in time for a given UE necessarily become scarce due tothe need to resort to large-scale time multiplexing of the usersdedicated SR resources (e.g. a user's dedicated SR opportunity may ariseonly once every 40 or 80 ms or so).

The approach of relying on time-domain multiplexing to support a largeconnected mode population causes a problem in that access latency isthen increased, since there is a high probability that the UE cannotsend the SR immediately following the arrival of new data in the buffer.It is clear therefore that with the dedicated SR approach, a trade-offalways exists between the amount of resources consumed or reserved, andthe access latency. An example of this type of problem is shown in FIG.5, where in this case, an SR opportunity 510 occurs only every 40 ms fora particular UE. If data arrives for UL transmission in-between theopportunities, the UEs need for UL transmission resources (on PUSCH)cannot be communicated to the eNB until the next opportunity—a timeperiod of up to 40 ms.

Furthermore, when attempting to achieve low latency access, (requiringfrequent DSR opportunities), the utilisation of those resources (i.e.occasions when a Scheduling Request (SR) is actually sent) reduces for agiven offered SR load. For many common traffic profiles, a UE may sendSR relatively infrequently and DSR resources are likely to be heavilyunderutilised. It can often be the case that less than 1% (even lessthan 0.1%) of the DSR resources are actually used by the UE to send SRand this may detract from overall system efficiency. If these unutilisedresources were not reserved for DSR, they could have been reassigned forother purposes, such as for the transmission of user data or controldata on UL, hence system capacity could have been improved.

Hence, it would be preferable to enable a scheduling request approach(intended primarily for connected mode users but not limited to such)which has the following attributes:

-   -   low access latency    -   use of an orthogonal multiple access scheme    -   efficient use of UL resources and high resource utilisation        RACH

One known alternative to the dedicated SR approach is the use of theexisting random access procedure to inform the eNB of a UE's need foruplink resources. This is a multi-step procedure, as illustrated in FIG.6, and is designed to transmit minimal information during the initialcontention phase, step 610. In order to minimise the information sent,step 610 does not include the transmission of a user ID. In step 620,the eNB 102 responds with an uplink grant of resources for each detectedpreamble from step 610. Access contention may remain during message 3,step 630 and the contention resolution message of step 640 is used toresolve the contention between any users who selected the same initialpreamble during step 610. The contention resolution message 640 may notbe sent if the message 3 630 that is successfully decoded by the eNB wasfrom a connected mode UE. In this case, the presence of the UL grantmessage 650 (addressed to the UEs C-RNTI) is sufficient to resolvecontention and allow uplink data transmission 660.

Whilst the RACH procedure is relatively efficient, it does involvemultiple steps and this can increase the access latency. Under someconfigurations, it also relies on a non-orthogonal multiple accessscheme (which offers reduced capacity compared to the orthogonal PUCCHand PUSCH multiple access schemes). Furthermore, a portion of theresources on PRACH are expended in providing time guard regions andfrequency guard regions to avoid interference from RACH users into othertime/frequency UL resource regions of the system (such as PUCCH orPUSCH). Hence, again, resource usage efficiency for PRACH can besub-optimal.

Furthermore, LTE PRACH occupies a wide bandwidth in the frequency domain(6 Physical Resource Blocks—PRBs). Thus, the provision of frequent RACHopportunities in time (to provide lower latency access) can then occupya large proportion of the over uplink resource space. Therefore, theexisting RACH procedure is designed more for initial access purposes andis not optimised for low-latency connected-mode scheduling requestpurposes.

SUMMARY OF THE INVENTION

In certain embodiments there is provided a method implemented in a userequipment UE for use in a wireless system for single carrier frequencydivision multiple access SC-FDMA, the method comprising, receiving anassignment of a scheduling request resource in the wireless systemcomprising a plurality of subcarriers; encoding a user ID; andtransmitting an uplink control channel signal comprising the encodeduser ID on the plurality of subcarriers of the assigned schedulingrequest resource.

In certain embodiments there is provided a user equipment UE for asingle carrier frequency division multiple access SC-FDMA system, the UEoperable to perform the method.

In certain embodiments there is provided a wireless system comprising atleast one such UE.

In certain embodiments there is provided a computer-readable mediumcomprising executable instructions that upon execution by a deviceperform the method.

In certain embodiments there is provided a method implemented in a userequipment UE for a wireless telecommunications system comprising:receiving an assignment of a scheduling request resource comprising aplurality of subcarriers; determining a need to transmit on scheduleduplink resources; encoding a user ID to generate encoded bits;modulating the encoded bits to produce modulated symbols; spreading themodulated symbols; mapping each of the spread modulated symbols to theplurality of subcarriers; and upon determining a need to transmit onscheduled uplink resources, transmitting an uplink control channelsignal comprising the plurality of subcarriers of the assignedscheduling request resource.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the present proposed approach will now be described indetail with reference to the accompanying drawings, in which:

FIG. 1 shows an LTE Radio Access Network coupled to an EPC core network

FIG. 2 shows an example arrangement of PUSCH and PUCCH resource blockswithin an uplink bandwidth;

FIG. 3 shows the composition of a MAC transport block;

FIG. 4 shows the structure of a scheduling request using PUCCH format 1;

FIG. 5 illustrates the difficulty of multiplexing dedicated SRopportunities for large numbers of UEs;

FIG. 6 illustrates the steps of a RACH procedure;

FIG. 7 illustrates the steps of a proposed SR method using PUCCH signalconstruction;

FIG. 8 illustrates the frequency multiplexing of common SR resourceswith UE-dedicated PUCCH resources;

FIG. 9 illustrates the time multiplexing of common SR resources withUE-dedicated PUCCH resources;

FIG. 10 illustrates the code multiplexing of common SR resources withUE-dedicated PUCCH resources;

FIG. 11 is a simplified block diagram of FEC encoding for PUCCH format2;

FIG. 12 is a simplified block diagram showing two possible methods ofperforming FEC coding where a plurality of PUCCH transmissions arerequired;

FIG. 13 illustrates the time domain separation of CSR resources;

FIG. 14 illustrates the orthogonality of time, frequency and codeseparations;

FIG. 15 is a block diagram showing the steps for constructing part of aPUCCH format 2 sub-frame;

FIG. 16 is a block diagram showing the steps of constructing part of aPUCCH format 2 sub-frame, modified for sending user ID information;

FIG. 17 is a block diagram showing the steps for constructing part of aPUCCH format 3 sub-frame;

FIG. 18 is a block diagram showing the steps for constructing part of aPUCCH format 3 sub-frame, modified for sending additional information;

FIG. 19 is a simplified block diagram illustrating the CRC attachmentand FEC encoding steps for a proposed variant of PUCCH format 2;

FIG. 20 is a block diagram indicating alternative CRC attachment optionswhere a plurality of PUCCH transmissions are required;

FIG. 21 is a block diagram showing a two-user CSR transmission scenariowhere collision occurs;

FIG. 22 is a block diagram showing a two-user CSR transmission scenariowhere collision does not occur;

FIG. 23 illustrates the steps of a proposed explicit SR mode switch withpre-configuration of resources;

FIG. 24 illustrates the steps of a proposed explicit SR mode switchwithout pre-configuration of resources;

FIG. 25 illustrates the steps of a proposed implicit SR mode switch withpre-configuration of resources;

FIG. 26 is a simplified block diagram illustrating a proposed SR modeswitching decision;

FIG. 27 illustrates the steps of a proposed UE SR mode change requestwith pre-configuration of resources; and,

FIG. 28 illustrates the steps of a proposed SR method using PUSCH signalconstruction.

FIG. 29 shows a number of example MAC PDU constructions for CSRtransmissions.

FIG. 30 illustrates an example SR transmission procedure.

DETAILED DESCRIPTION

PUCCH

In certain embodiments, a common or shared SR resource (CSR-resource) isassigned to a plurality of users for the purposes of sending schedulingrequests that contain a user ID or part thereof. The CSR resource mayreuse existing physical layer control channel (PUCCH) formats for therevised purpose of sending the SR containing the ID or part thereof. Thereuse of existing LTE PUCCH format types (not originally designed forcontention-based SR purposes) to carry the user ID reduces the need forphysical layer redesign and enables the scheme to be used on existing orlegacy hardware or firmware implementations. The scheme may use PUCCHformats capable of carrying more bits than the current PUCCH formats1/1a/1b in order to allow a large number of users to share the samePUCCH resource.

Certain embodiments comprise explicitly sending a user ID (or portionthereof) to the eNB within a PUCCH signal construction (e.g. PUCCHformat 2 or PUCCH format 3) during the access attempt on a common orshared resource assigned for contention-based scheduling request (CSR)purposes. Typically the resources assigned for this purpose will residewithin the control (“PUCCH”) frequency region of the uplink systembandwidth, although it is also possible that the resources are allocatedwithin the data (“PUSCH”) frequency region, or even entirely with thedata (“PUSCH”) frequency region. It can be required that only some ULresources are assigned to a plurality of users for the purposes ofsending the user ID bits using PUCCH format signal constructions.

FIG. 7 shows the steps taken in certain embodiments:

-   -   1) As a precursory first step 710, an eNB optionally assigns a        portion of uplink resources (in either the control (PUCCH) or        data (PUSCH) frequency region) to a plurality of UEs for the        purposes of contention-based scheduling request. The resource        assignment may be conveyed via broadcast signalling or may be        signalled individually to each of the plurality of UEs. This        first step may be omitted if the resources are pre-defined, for        example in a standard.    -   2) At some later point in time, pending data arrives in the UEs        transmission buffer 720    -   3) The UE encodes a user ID (or portion thereof) using a PUCCH        signal construction method (e.g. PUCCH format 2 or 3), and        transmits 730 the signal on the assigned CSR resource    -   4) An eNB receiver decodes 740 at least the UEs transmitted        signal from the CSR resource, and subsequently derives the UE ID        using the decoded information.    -   5) The eNB proceeds to send a normal UL-grant message 750 to the        UE to allocate it a portion of PUSCH resource for the        transmission of data. The UL-grant message is conveyed in a        Downlink Control Information (DCI) message sent over a Physical        Downlink Control Channel (PDCCH).    -   6) The UE then has access to PUSCH and is able to send its data        760 to the eNB.

Compared to the RACH procedure in FIG. 6, the method shown in FIG. 7involves fewer steps and therefore allows for a lower-latency schedulingrequest procedure.

The current LTE system uses PUCCH format 1 to carry dedicated SR. Theunderlying principle of dedicated SR transmission is that the usersending the scheduling request is distinguished by means of theparticular (i.e. user-dedicated) time/frequency/code resources on whichthe SR was sent, rather than by means of sending an explicit ID viatransmission bits that are demodulated by the eNB receiver.

The use of a contention-based resource (i.e. a common or shared portionof uplink time/frequency/code resource) for SR can significantlyincrease the resource efficiency of the SR access scheme when comparedto the dedicated SR approach (even whilst achieving similar or betterlatency of access). However, when using a contention-based resource, theuser sending the SR can no-longer be inferred by the eNB solely from thetime/frequency/code resources on which the SR was sent. To minimiselatency, and to reduce access contention it is preferable for the userID (or part thereof) to be explicitly communicated to the eNB during theinitial SR message sent by the UE on the CSR uplink resource.

PUCCH—Multiplexing

The CSR resource may be a portion of the PUCCH or PUSCHcode/time/frequency region of the overall UL system resources of a cell(the overall UL system resources of a cell may optionally also comprisemultiple component SC-FDMA carriers). Multiple UEs are provided orconfigured (e.g. by the eNB) with an allowance to transmit SR on thesame CSR resource should they need to indicate that access to the PUSCHis required. The configuration provided by the eNB that defines thetime, frequency and code locations of the CSR resource may be one of:

-   -   predefined (within a standard)    -   signalled to all UEs within a cell via broadcast system        information    -   signalled to a UE via one-to-one (dedicated) signalling

For example, if PUCCH resources are assigned for contention-based SR(CSR), multiple users may be assigned the same PUCCH format 2 resourceindex n_(PUCCH) ^((2,p)) (or the same resource index for another PUCCHformat type, such as n_(PUCCH) ^((3,p)) for PUCCH format 3).

The signalling providing the configuration of the CSR resource wouldpreferably occur between peer RRC entities in the eNB and UE(s)respectively, but may also take place between peer MAC or physical layerentities of the eNB/UE(s). If the signalling occurs at RRC level, thesignalling may reuse or partially reuse RRC signalling structures andmessages, such as those used for dedicated SR, CQI, or SPS configurationin the current LTE system (with the same resource configuration beingprovided to each UE). Alternatively, modifications to the existingmessages may be required in order to support configuration of the CSRresource.

Generally, the CSR resource may be time, frequency, or code multiplexedwith user-dedicated PUCCH resource (such as may be used for dedicated SRor for the sending of channel state information such as CQI/PMI/RI) orwith other resources such as PUSCH allocations. This allows for the newCSR scheme to be smoothly integrated into existing systems in whichother PUCCH or PUSCH resources may continue to be used for such otherpurposes.

An example wherein the common/shared SR resource is frequencymultiplexed with dedicated PUCCH resource is shown in FIG. 8. In linewith the current design in LTE, each square block corresponds to oneResource Block (RB) of frequency resource and one slot (0.5 ms) of timeresource. Two 0.5 ms slots comprise one 1 ms sub-frame of time resource.

PUCCH resources reserved for UE-dedicated purposes are labelled D1, D2,. . . D8 810, with each comprising two slots of transmission. As per thecurrent LTE design, one of two slots belonging to the same PUCCHtransmission is transmitted in the upper 840 or lower 830 PUCCH controlregion, whilst the other slot is transmitted within the opposite (lower830 or upper 840 respectively) PUCCH control region. This may be used inorder to provide frequency diversity and improved reliability of PUCCHreception.

PUCCH transmission opportunities for the new CSR are labelled C1, C2, .. . C8 820, with each PUCCH comprising the same two-slot transmissionarrangement in the upper 840 and lower 830 (or lower 830 and upper 840)PUCCH control regions. C1 . . . C8 820 are frequency multiplexed with D1. . . D8 810 in that they occupy different RBs within the overall systembandwidth of the uplink.

An alternative multiplexing arrangement is shown in FIG. 9 whereincommon/shared SR resources on PUCCH 920 (denoted C1 . . . C8) are timemultiplexed with UE-dedicated PUCCH resources 910 (denoted D1 . . . D8).An example of time multiplexing is shown here at the sub-frame levelalthough time multiplexing at the slot level is also possible.

A yet further alternative multiplexing arrangement is shown in FIG. 10wherein common/shared SR resources on PUCCH 1010 (denoted C1 . . . C8)are code multiplexed with UE-dedicated PUCCH resources 1020 (denoted D1. . . D8). The code multiplexing may be achieved for example via theassignment of cyclic shifts (or cyclic shift patterns) of afrequency-domain spreading sequence for the common/shared PUCCH resourcethat are different within a sub-frame and resource block to thoseassigned to the UE-dedicated PUCCH resource. The code multiplexing couldalso be achieved via the use of different time-domain code sequences ordifferent 2D time-frequency codes for the common/shared PUCCH 1010resource and the UE-dedicated PUCCH resource 1020.

Combinations of the frequency multiplexing, time multiplexing and codemultiplexing schemes of FIG. 8, FIG. 9, and FIG. 10 respectively mayalso be used.

The CSR resource (conveying PUCCH-like SR signals) may also residewithin the PUSCH frequency region 240, and may be multiplexed with otherPUSCH transmissions in either the time or the frequency domain. Ascheduler within the eNB may take into account the presence or absenceof the CSR resource within a given time/frequency resource space whendetermining the availability of upcoming PUSCH resources and whenallocating those resources to UEs. For example, the eNB scheduler maydetermine not to dynamically schedule a PUSCH resource to a UE if thatPUSCH resource is instead reserved for CSR transmissions.

To carry a set of bits that explicitly convey the user ID (or partthereof), one of the existing PUCCH formats that carries a plurality ofbits for demodulation (for example used in the existing system to conveyCQI or other channel state information (CSI), or to carry multiple HARQACK/NACK feedback bits) can be reused for the purposes of sending an SR(containing the explicit bits) on the CSR resource.

Primary candidates from the set of existing PUCCH formats to use forthis new purpose of sending an explicit user ID are PUCCH format 2 andPUCCH format 3. Other new or modified PUCCH formats having potentiallydifferent payload sizes may also be considered, as may variants ofexisting PUCCH formats (e.g. formats 2a and 2b).

PUCCH format 2 is used in the existing LTE system to send CQI/PMI/RIreports. When reusing PUCCH format 2 for the purposes of sending a userID during CSR, instead of transmitting channel state information such asCQI/PMI/RI, an ID unique to the transmitting user (denoted hereCSR-uRNTI) and comprising N_(ID) bits is encoded and transmitted via oneor more PUCCH format 2 transmissions. The number of PUCCH transmissionsrequired to convey the whole of the user ID is equal to:N _(TX) =┌N _(ID) /A┐where A is the bit payload available within the PUCCH format underconsideration. For example, A may be 13 for PUCCH format 2, constrainedin this case by the maximum input length to the [20,A] FEC block encoder1110 as illustrated in FIG. 11 where A (13) input bits 1101 would be FECencoded to 20 output bits 1102. However, various values of N_(ID) and Amay be used.

In the LTE system, connected mode users are allocated a Cell RadioNetwork Temporary Identifier (C-RNTI) comprising 16 bits and in oneexample, the user ID used for CSR purposes (CSR-uRNTI) may be set equalto the C-RNTI, and hence N_(ID)=16.

For these larger values of N_(ID) (for example N_(ID)=16) the N_(ID)bits could be transmitted using one or more than one PUCCH transmission.If more than one PUCCH transmission is used, two options exist forcarrying N_(ID) bits over the plurality of PUCCH transmission instances:

-   -   i. The N_(ID) bits 1210 are segmented 1220 into N_(TX) groups        and each is separately FEC encoded 1230 and mapped to its own        PUCCH transmission instance 1240 within a sub-frame, as        illustrated in FIG. 12( i) for N_(TX)=2.    -   ii. The N_(ID) bits 1250 are input to a single (and modified)        FEC encoder 1260 and the output bits are segmented 1270 into        N_(Tx) groups which are subsequently mapped to their own PUCCH        transmission instances 1280, each within a sub-frame, as        illustrated in FIG. 12( ii) for N_(TX)=2.

For example, for the case of A=8, there would be a need for N_(TX)=2PUCCH transmissions in order for a user to transmit a 16-bit CSR-uRNTIon the CSR resources to the eNB (i.e. the ID is carried using twosegments). The transmission segments could be transmitted on adjacent ornon-adjacent sub-frames). The eNB would need to know which of the two(or multiple) PUCCH transmissions carries the first segment in orderthat the full CSR-uRNTI may be correctly reassembled. For example, theresources carrying the new PUCCH SR could be organised in pairs ofresources separated in frequency/code/sub-frame or otherwise so that theeNB could easily reassemble the complete message once the resource pairhas been received. To do so, it is conceivable that certain sub-framesavailable for CSR are designated as starting sub-frames, in which userstransmit the 1st segment of a multiple-segment PUCCH transmissioncarrying a user ID (the remaining segments being transmitted thereafterin other sub-frames existing in-between successive starting sub-frames).Furthermore, the starting sub-frames could be different for each user,this being signalled explicitly to each user, or being derived as afunction of a user ID.

Alternatively, it may be preferable to restrict the necessary number ofPUCCH transmissions to 1 (no segmentation), in which case theinformation payload of the PUCCH must be greater than or equal to N_(ID)bits. If PUCCH format 2 is used, the following possibilities exist:

-   -   1) N_(ID)>13 (e.g. N_(ID) is equal to the C-RNTI length of 16        bits)        -   a. A new [20,A] encoder supporting A>13 could be used (to            carry e.g. N_(ID)=16 bits)        -   b. The modulation level for PUCCH format 2 could be            increased from QPSK to (for example) 16-QAM, thereby            allowing for 40 encoded bits to be carried            -   i. This could be used in conjunction with a new [40,A]                code, or reuse of the existing [20,A] code with                repetition (or similar post processing of outputs from                one or more [20,A] codes)    -   2) N_(ID) is constrained to be ≦13 (in order to comply with        max(A) δ13 for the existing FEC block encoder)

In case (2) above, it could be possible that the eNB assigns to the UE aCSR-uRNTI that is shorter than the C-RNTI (e.g. CSR-uRNTI ≦13 bits). Ingeneral, the CSR-uRNTI could be associated with or derived from theuser's C-RNTI. For example, the CSR-uRNTI could comprise a subset of the16 bits of the C-RNTI, or could be formed via one or more mathematicaloperations such as a hashing function using or based on the C-RNTI (orother RNTI or ID). The CSR-uRNTI could instead be signalled by the eNBto the UE explicitly within a signalling message addressed to the UE.Alternatively, parameters used in describing the linkage between auser's C-RNTI and the CSR-uRNTI could be transmitted to the UE (witheach user then deriving its own CSR-uRNTI based on the receivedparameter information and its knowledge of its own C-RNTI). Theparameters may be broadcast within a cell (sent within systeminformation transmitted by the cell), or may be sent to each UEindividually.

A further option under case (2) above is that a portion (e.g. ≦13 bits)of a longer user ID is explicitly conveyed via the PUCCH formattransmission, whilst the remaining bits are carried or are otherwiseknown implicitly. FIG. 13 illustrates a scheme of time-domainsegmentation of CSR resources used for carriage of implicit UE ID bitswhere a user ID length is required to equal to 16 bits (e.g. C-RNTI).Here 13 bits of the C-RNTI could be carried explicitly via a PUCCHformat 2 transmission within one sub-frame (i.e. A=13), whilst theremaining 3 bits could be associated with one of 2³=8 possible sub-framelocations 1310. In this example, CSR resources that are assigned by theeNB are divided into 8 groups, each group being associated with asub-frame index within a set of 8 CSR sub-frames, and each sub-frameindex being associated with a particular realisation of 3 C-RNTI bits(000, 001, 010, . . . 111). A UE therefore knows to associate its UE IDwith one of the 8 sub-frame indexes and elects to transmit its CSR onlyon sub-frames having that index. Thus, on reception and decode of anexplicit 13 bit sequence (partial ID) on a given sub-frame index, theeNB is able to determine a full 16-bit UE ID and to schedule PUSCHresources to that UE (for example using the UEs C-RNTI) accordingly.Note that although the sub-frames are shown as adjacent in time, thesemay also be separated by intervening periods of time (sub-frames) onwhich no CSR resources are allocated (for any user) by the eNB.

Whilst the advantage of this time-multiplexing scheme is that the wholeUE ID is transmitted within 1 sub-frame (some bits are carriedexplicitly whilst others are implicitly conveyed via selection of theappropriate sub-frame), as a result there may be an increase in latencycompared to the case where the whole UE-ID can be transmitted on anysub-frame meant for the CSR resource (i.e. the need to introduce thetime-multiplexing component may also increase the scheduling requestlatency).

Extensions to this scheme of partial-ID explicit transmission(supplemented by implicit conveyance of the remaining bits) are alsopossible utilising not only time-domain separation of resources toimplicitly convey the additional bits, but also (or in substitute) usingfrequency or code domain resources separations to do so. Notably, byusing code or frequency domain multiplexing instead of timemultiplexing, this may avoid the introduction of any increase to thescheduling request latency, whilst still enabling conveyance of the fulluser ID via a mix of explicit and implicit signalling.

Thus, in another example, 12 bits of a 16-bit user ID could beexplicitly signalled within a PUCCH transmission, and the remaining 4bits could be conveyed via selection of one of 2⁴=16 time/frequency/coderesources. These 16 separated resources could comprise for example 2sub-frames in the time domain 1410, 2 resource blocks in the frequencydomain 1420 and 4 cyclic shifts of a frequency domain spreading code1430. Thus, the total number of separated resources is 2×2×4=16. Such ascheme is shown in FIG. 14 although it will be appreciated that numerousvariations are possible, involving varying degrees of time domain,frequency domain and code domain resources. Schemes involving onlyfrequency-domain separation, only code domain separation or only timedomain separation are all possible. Furthermore, for the case ofcode-domain separation, the individual codes may be formed via timedomain spreading, frequency domain spreading, or both (2D codes).

If it is preferable to transmit a larger user ID using explicit means,and to also avoid the need for segmentation into multiple PUCCHtransmissions, a further option is to employ a PUCCH format with alarger payload capacity than PUCCH format 2. For example, if theCSR-uRNTI is set equal to the C-RNTI and all 16 bits are to betransmitted explicitly in full, the existing PUCCH format 3 could beemployed, which is capable of carrying A=21 bits via a payload of 48encoded bits and offering a user multiplexing capability of 5 users perRB within a sub-frame.

In cases where the payload size allows, in addition to the CSR-uRNTI orC-RNTI bits, there is a possibility to transmit additional data alongwith the user ID bits. For example, the data could be other controlinformation, such as CQI/PMI/RI or buffer status information, or couldbe a small amount of user-plane data. Alternatively, only the user IDbits could be sent via the PUCCH format 3 transmission.

PUCCH Format 2

Similarly, existing PUCCH formats could be adjusted in order to supporthigher-order modulation levels (higher than the current QPSK). Forexample, use of 16-QAM on PUCCH format 2 would retain the same PUCCHcode multiplexing capability (maximum of 12 possible cyclic shifts ofthe frequency domain spreading code) whilst simultaneously enablingtransmission of 40 encoded bits. A new FEC code (e.g. [40,16]) couldthen be used to convey all 16 bits of a C-RNTI user ID, or all bits of aCSR-uRNTI. Again, the additional payload space available could be usedto carry other control information (such as CQI/PMI/RI, or buffer statusinformation) or even to carry user plane data in addition to the user-IDbits included in the scheduling request transmission.

FIG. 15 shows the construction of an existing PUCCH format 2 signal (forsome blocks, only the 1^(st) slot of a 2-slot sub-frame is shown). “A”input bits (A<=13) are input to an FEC encoder 1510 which outputs 20encoded bits. These are scrambled using a UE-specific bit scramblingsequence, generated by bit scrambling sequence generator 1520 as afunction of the UEs C-RNTI. The 20 scrambled bits undergo QPSKmodulation 1540 to form 10 modulation symbols (5 modulation symbols d(0). . . d(4) for the 1^(st) slot and 5 modulation symbols d(5) . . . d(9)for the 2^(nd) slot). Each of the modulation symbols are separatelymapped to a corresponding one of 10 SC-FDMA symbol branches (5 perslot). For each branch, the modulation symbol is spread using alength-12 frequency domain “base” spreading sequence generated bygenerator 1550. A cyclic shift 1560 is applied, wherein different cyclicshifts may be applied to different SC-FDMA symbol branches, the cyclicshifts being determined by a pseudo-random function of a cell ID, a slotnumber, and the symbol number that corresponds to each SC-FDMA symbolbranch. Unlike the bit scrambling sequence, the pseudo random functionthat determines the cyclic shifts is cell specific, as it depends on acell ID rather than an ID assigned to a UE, such a C-RNTI. The result ofeach cyclic shift operation is input to an IFFT 1570 in order to formthe corresponding SC-FDMA symbols 1580. A cyclic prefix (CP) ispre-pended to each SC-FDMA symbol.

FIG. 16 shows an overall view of how PUCCH format 2 could be modified tosend explicit bits of a user ID. N_(TX) bits of the full user ID (oflength N_(ID)) are input to an FEC encoder 1610, where N_(TX)≦N_(ID).Depending on the sizes of the input and output of the FEC encoder, theexisting [20,A] block code may be reused, or a new block code (orencoding scheme based on one or more constituent block codes) withdifferent supported input and output lengths may be used. A furtheralternative is that no FEC encoder is used or a simple repetition codeis employed. Further coding schemes are possible within this generic FECencoding block, for example convolutional codes (tail-biting ornon-tail-biting), turbo codes, or low density parity check (LDPC) codescould be employed.

Due to the fact that the modified PUCCH format 2 will not be sent ondedicated SR resources, the output bits from the FEC encoder need not bescrambled with a user specific scrambling sequence. This is because theeNB receiver does not know which user(s) will transmit on the CSRresource. Instead, a bit scrambling sequence is used that is common toall (or multiple) users who may transmit on the same CSR resource of acell. The scrambling sequence may be generated by a scrambling sequencegenerator 1620, and the generator may be initialised with a value.However so derived, the scrambling sequence may be based upon one ormore of: a CSR group RNTI (CSR-gRNTI), a cell ID, a sub-frame index, atime-slot index. Alternatively, a specific or predefined scramblingsequence may be used. In other embodiments, a cyclic-shift-specific orcode-specific scrambling sequence may be used. In yet furtherembodiments, a sub-frame or resource-block specific scrambling sequencemay be used. It is also possible that no bit scrambling is employed(i.e. the modulo 2 addition block 1630 is absent from FIG. 16), orequivalently, the bit scrambling sequence is set to “all zeros”. All ofthese non-user-specific bit scrambling schemes advantageously allow theeNB receiver to perform the descrambling operation before it hasidentified the user(s) who have transmitted an SR on the CSR resource ofa cell, thereby avoiding the need to blindly determine the scramblingsequence used and simplifying the eNB receiver.

The output from the bit scrambling block (modulo 2 addition block 1630)or alternatively the direct output from the FEC encoder 1610 (if no bitscrambling is employed), are input to a modulation block 1640 in orderto form complex output symbols d0 . . . d4 (for the 1st slot of asub-frame) or symbols d5 . . . d9 (for the 2nd slot of a sub-frame). Themodulation block may implement QPSK or may implement another form ofmodulation such as BPSK, 8-PSK, or 16-QAM.

The modulated symbols are spread using a frequency domain spreadingsequence 1650 (for example, of length 12 such that the symbol occupiesone Resource Block—RB—of frequency resource). Each symbol may use thesame or a different cyclic shift of the same spreading sequence. In bothcases, a “base” cyclic shift may be selected by the UE, possibly atrandom from an allowed set of base cyclic shifts. If each symbol usesthe same cyclic shift 1660, the base cyclic shift is applied to eachsymbol. In the case that different cyclic shifts are employed ondifferent symbols, the base cyclic shift may be permuted for each symbolin accordance with a cell-specific cyclic shift hopping pattern. Thehopping pattern may be based upon a pseudo-random sequence generator(not explicitly shown) as is used within the current specifications forPUCCH format 2 and described with respect to cyclic shift 1660.Alternatively, no cyclic shift hopping may be employed. Following thefrequency domain spreading operation, an IFFT operation 1670 isperformed on each frequency-domain symbol in order to form time domainSC-FDMA symbols 1680 for transmission. A cyclic prefix is added to eachSC-FDMA symbol via copying of an end portion of the symbol andpre-pending the copied end portion to the start of the symbol.

Comparing FIG. 16 with FIG. 15 shows more clearly the modifications madeto the PUCCH format 2 constructions. At the block encoder 1510, theunmodified PUCCH format 2 construction takes channel state information(CQI/PMI/RI) as the input rather than user ID information. The bitscrambling sequence generator 1520 is based only on UE-specific C-RNTIand there is no option not to utilise bit scrambling and modulo 2addition 1530. Additionally, in FIG. 15 the FEC encoder 1510 andmodulation block 1540 are unmodified whereas the corresponding blocks ofFIG. 16 FIG. 15 may be modified. Furthermore, the frequency domainspreading sequence 1650 and/or the cyclic shift(s) 1560 of FIG. 15 maybe selected (for example at random) from an allowed set by the UE. Theallowed set may be associated with a cell or with a specific CSR time orfrequency resource within a cell.

PUCCH Format 3

Due to its limited payload size, there is little room (without using ahigher order modulation or a new FEC code) within the current PUCCHformat 2 construction to transmit a CRC or other information in additionto a user ID (although this is not precluded). However, PUCCH format 3has a higher payload size and this can allow greater potential foradditional information to be carried alongside the user ID. FIG. 17shows the construction of an existing PUCCH format 3 signal (for someblocks, only the 1^(st) slot of a 2-slot sub-frame is shown). Up to 20ACK/NACK bits are input to an FEC encoder 1710 which outputs 48 encodedbits. These are scrambled using a UE-specific bit scrambling sequence,generated by bit scrambling sequence generator 1720 as a function of theUEs C-RNTI. The 48 scrambled bits undergo QPSK modulation 1730 to form24 modulation symbols (12 modulation symbols for the 1^(st) slot and 12modulation symbols for the 2^(nd) slot). The 12 modulation symbols forone slot are replicated for each of the slot's 5 SC-FDMA symbols, andfor each of these SC-FDMA symbol branches, the symbols are multiplied bya corresponding element of a length-5 orthogonal cover sequence 1750. Acyclic shift 1760 is applied that is determined by a cell specificpseudo random function similar to that used in cyclic shift generator1560. The result of each cyclic shift operation is input to a DiscreteFourier Transform (DFT) operation. For each SC-FDMA symbol branch theoutput of the DFT is input to an IFFT 1770 in order to form thecorresponding SC-FDMA symbols 1780.

FIG. 18 shows the modified coding of a traditional PUCCH format 3 (FIG.17) to send up to 16 bits of CSR-uRNTI (e.g. C-RNTI) and optionally someadditional bits (up to 5) whilst still reusing the existing PUCCH format3 construction comprising FEC encoder 1810, bit scrambling sequencegenerator 1820 and modulation block 1830. Note that unlike the PUCCHformat 2, coding an orthogonal cover sequence 1850 of length 5 isapplied to the modulated symbols before the SC-FDMA transformation. Theadditional 5 bits of space available could be used for instance to add aCRC to the transmitted C-RNTI, to send channel state information (suchas CQI/PMI/RI), or to send other data such as buffer status informationor even small amounts of user data. If higher order modulation is used(eg: 16/64 QAM), further additional bits can in theory be transmitted.Like in traditional PUUCH format 3, after the cover sequence 1850 isapplied, a cyclic shift 1860 is applied, followed by a DFT operation andthen input to an IFFT 1870 to form the corresponding SC-FDMA symbols1880.

CRC Attachment

Within the payload of bits carried by a contention-based-SR PUCCHformat, a cyclic redundancy check (CRC) may also be employed. This mayhelp for example to reduce the probability of false alarm or incorrectdetection of the UE ID at the eNB. In this variant the input to the FECencoder is altered to allow for CRC bits to be included.

False alarms occur when the eNB detects a valid scheduling request on aparticular SR resource but no SR was sent on that resource. Variousmethods of reducing the occurrence of false alarms may be employed, suchas measuring the received power of data or reference signals andcomparing the measured power to a threshold in order to decide whetheran SR transmission was present or absent.

Methods such as these may also be augmented (or substituted) withalternative schemes based on the use of a CRC to help discriminatebetween the presence and absence of an SR transmission. In general thenumber of CRC bits used may therefore be dependent on:

-   -   the number of user ID bits being carried    -   the level of false alarm protection required    -   the performance of complimentary (i.e. non-CRC-based) solutions        to the false alarm problem

If no other false-alarm avoidance measures are adopted, relatively longCRCs may be required. For example, if a 0.1% false alarm probability wasdesired, a 10-bit CRC may be needed to ensure a 1/1024 false alarm rate.Conversely, the number of CRC bits could be considerably reduced (or theneed for a CRC could be eliminated) if other complimentary non-CRCmethods are employed to reduce the false alarm rate.

The addition of an increased number of CRC bits reduces the spaceavailable for FEC coding redundancy for a constrained number of codedoutput bits. Thus, the number of CRC bits must be traded-off against FECprotection.

If CRC bits are included prior to encoding, the block encoding step(which accepts an input of A input bits) is preceded with a CRC encoder.As shown in FIG. 19, the CRC encoder 1910 accepts an input of A′ bitsand outputs A bits to the block encoder 1920, where A=A′+N_(CRC).

In the example of PUCCH format 2 , 1≦A≦13, and the block encoder 1920that follows the CRC addition stage 1910 then produces an outputcodeword of length 20 bits. As has been previously described, the lengthof the input and output of the block encoder may vary for other existingor modified PUCCH formats.

As described previously, the N_(ID) bits could be transmitted using oneor a plurality of PUCCH transmission instances. With reference to FIG.12, if more than one PUCCH transmission is used, the N_(ID) bits may beeither segmented 1220 into N_(TX) groups prior to separate FEC encoding1230, or the output of a single encoder 1260 may be segmented 1270 intoN_(TX) groups. In either case, the bits corresponding to each of theN_(TX) groups may then be carried via a PUCCH transmission instancewithin a sub-frame. FIG. 20 illustrates three options for deriving theCRC:

-   -   i) One CRC 2010 is calculated-over (and appended to) the full        N_(ID) bits. Following segmentation 2020, the resulting bits are        transmitted over the N_(TX) PUCCH transmission instances, each        using separate FEC encoding stages 2030    -   ii) One CRC 2040 is calculated-over (and appended to) the full        N_(ID) bits. The resulting bits undergo a common FEC encoding        stage 2050 and following segmentation 2060, are transmitted over        the N_(TX) PUCCH transmission instances.    -   iii) The N_(ID) bits are first segmented 2070 into N_(TX) PUCCH        transmission instances. A CRC is calculated 2080 per PUCCH        transmission instance and separate FEC encoding stages 2090 are        used for each.        Collision Aspect

Some embodiments of the scheme may be intentionally designed in order tominimise the need for changes (e.g. at the physical layer, MAC or RRClayers) to the existing LTE system. If existing PUCCH formats can bereused for the purposes of sending a user ID or part thereof, it ispossible not only to reuse much of the existing UE transmissionarchitecture but also to minimise or even eliminate the need for changesto some of the eNB receiver layers (in particular, the physical layer).That is, the reuse of existing PUCCH formats to convey a user ID or partthereof, may not require modifications to the eNB physical layer, andneed only allow passing of the demodulated and decoded user ID to theeNB scheduler in order that the UEs request for access to PUSCHresources may be taken into account in the upcoming schedule.

When a UE determines a need to send a scheduling request on the CSRresources, there is the possibility that another UE with allowance touse the same CSR resources, also sends an SR at the same time (i.e.within the same sub-frame). If the two transmitting users selectdifferent frequency or code assignments within the same sub-frame, thetwo scheduling requests remain separable by the eNB and, followingdemodulation and decoding of each, the eNB scheduler may grant bothusers with access to PUSCH (sending a separate PDCCH message to eachuser on downlink).

However, there is also the possibility that two (or more) users transmita scheduling request on the same time (sub-frame), frequency and coderesources. In this situation, different user IDs (or parts thereof) aresent on the same resource and the transmissions may not be easilydistinguishable or separable by the eNB receiver (although more advancedtechniques based upon spatial separation of the signals may beimplemented). For simplicity, it may be preferred that no changes arerequired for the eNB receiver's physical layer processing and in thiscase, the eNB will attempt to decode the received “composite” signal(comprising the transmissions from both UEs) as a single UEtransmission.

Each transmitted user signal s_(u)(t) (with “u” in this two-user casetaking values of 1 or 2), will be subject to modification en-route tothe eNB by the intervening radio propagation channel with impulseresponse h_(u,k)(t) for the k^(th) receive antenna at the eNB (forsimplicity in this example, each UE has a single transmit antenna).

The composite received signal (arriving on a particulartime/frequency/code resource) comprises the linear superposition of thetwo signals received from each of the colliding UEs, and so at thek^(th) receive antenna, the received signal (ignoring the channel noise)is:r _(k)(t)=s ₁(t)

h _(1,k)(t)+s ₂(t)

h _(2,k)(t)

Schemes are possible in which UEs with colliding data transmissions usethe same or different reference signals. However, for the existing PUCCHformats, the time/frequency/code resources used for transmission of datasymbols have a predetermined relationship to the time/frequency/coderesources used for the demodulation reference signals (DMRS). If thisprinciple is maintained, colliding UEs will use the same resources fortheir data symbols in addition to using the same resources for theirDMRS.

In the case that the transmissions for the colliding UEs do use the samereference signals, the eNB receiver will (usually following FFTprocessing to transform the received time-domain signal into thefrequency-domain) form a frequency-domain channel estimate:Ĥ _(k) =FFT{h _(1,k)(t)+h _(2,5)(t)}+n

The term n is used here to represent channel estimation noise or error.

The eNB will then perform frequency-domain channel equalisation (to“undo” the effects of the channel as best as possible) and will combinethe signals received from each of its receive antennas. The resultingequalised and combined signal is then sent to further processing units.The further processing units may comprise operations equivalent-to orthe-inverse-of those known to have been employed by the UEtransmitter(s), including for example, one or more of:

-   -   A frequency-domain despreading unit    -   A time-domain despreading unit    -   A bit descrambling unit    -   A demodulation unit    -   An FEC decoder unit

The output of the FEC decoder (the decoded ID) is either directly usedby the eNB as the user ID (e.g. C-RNTI or CSR-uRNTI), or the C-RNTI isderived via a known association between the decoded ID and the C-RNTI.

It can be shown however, that in the absence of significant thermalnoise or other interference, the case wherein two users simultaneouslytransmit different IDs on the same time/frequency/code resource resultsin the decoded ID being equal to either the ID for user 1, or the ID foruser 2 (and not another ID). For this to occur, the following aspectsmay exist:

-   -   1. Both UEs use the same reference signals (RS)        -   a. UEs may have independently selected the same PUCCH            resource index, (e.g. n_(PUCCH) ^((2,p)) or n_(PUCCH)            ^((3,p)) or may have been configured to use the same            resource index value        -   b. UEs sending SR on the same CSR resource use the same            cyclic shift hopping patterns (e.g. cell-specific hopping as            is used for the current PUCCH formats) for the RS symbols            within a subframe, or alternatively no cyclic shift hopping            is employed for the RS symbols.    -   2. Both UEs use the same bit scrambling sequence during PUCCH        construction (or alternatively no bit scrambling is applied)        -   a. The common bit scrambling sequence may be based upon a            CSR-gRNTI, a cell-ID, or other resource-specific parameters.

In these circumstances, the decoded output is unlikely to be equal to anID other than that of either user 1 or user 2. This may be advantageousfor the SR transmission scheme, since in the event of a collision, theeNB will still determine that one of the users requires access to PUSCHresources (that is, it is not the case that both users destructivelyinterfere and both are lost).

Thus, when two or more users collide, the eNB still is able to schedulePUSCH resources for one of the users. The other (notreceived/not-decoded) user(s), will not receive an UL grant from the eNBand will attempt a re-try of its scheduling request at another CSRopportunity. To control SR retransmissions, the UE would typically beconfigured to set a prohibit timer to a predefined (or potentiallyrandomised) start value whenever an SR has been sent, and would attempta re-try only once the prohibit timer has expired.

FIG. 21 shows the case wherein two users 2101 and 2102 transmit (2111and 2112) part or all of respective user IDs (e.g. on PUCCH format 2)using the same time/frequency/code resources. In the example shown, thetwo users transmit the same reference signals and use the same bitscrambling sequences (or use no bit scrambling).

The processing steps implemented in the eNB receiver are also shown. TheeNB attempts to receive 2130, despread 2140, demodulate 2150, descramble2160 and decode 2170 a single user ID from the received signal on thetime/frequency/code resource used by both users. Even in the presence ofthe collision, the eNB may still be able to correctly detect one of thecolliding users 2180 and so this information may be used by the uplinkscheduler to allocate PUSCH resources to the successful user 2190.

FIG. 22 shows the case wherein two users 2101 and 2102 transmit (2211and 2212) part or all of respective user IDs (e.g. on PUCCH format 2)using the same time/frequency resources but using different coderesources. The two users do not transmit the same reference signals(i.e. different codes or cyclic shifts are used) and the two users mayor may not use the same bit scrambling sequences (or no bit scramblingmay be employed).

The processing steps implemented in the eNB receiver are also shown. TheeNB attempts to receive 2230 two user IDs on their respective coderesources, via despreading 2240, demodulation 2250, descrambling 2260and decoding 2270 operations. The eNB correctly detects 2280 both usersand so this information may be used by the uplink scheduler to allocate2290 individual PUSCH resources to each.

In both FIG. 21 and FIG. 22, the eNB receiver is designed to detect anddecode one user signal per designated time/frequency/code resource. Moreadvanced eNB receiver structures are conceivable in which the eNBattempts to detect and decode more than one user signal per designatedtime/frequency/code resource. These may for example, exploit certainspatial characteristics of the plurality of incident user signals.

SR Mode Switching

SR resource types may be switched in time for a given user between thoseof periodic or dedicated type (DSR), to those of common or shared type(CSR), and different users within the system or under control of an eNB,may use different types of SR resources. It is also possible that theuser may be switched between use of a first SR resource and a second SRresource, wherein both the first and second resources are ofcommon/shared type, or wherein both the first and second resources areof dedicated type.

For example, a user may be temporarily assigned dedicated SR resourceswhen in an active phase of communication (exchange of UL or DL datais—or has recently—taken place) and upon transitioning to a moreinactive phase of communication, this user-dedicated SR resource (DSR)may be released and the user instead uses the common or shared SRresource (CSR).

In one particular example, switching between use of DSR resources andCSR resources may be linked to a Discontinuous Reception (DRX) state orsub-state, or to operation of an inactivity timer (such as a DRXinactivity timer), or to another timer or parameter controlling a DRXpattern. In this case, a user may be assigned dedicated periodic SRresources on PUCCH whilst a DRX inactivity timer is running and onexpiry of the DRX inactivity timer (or at a time linked to the expiry ofthe DRX inactivity timer), the DSR resources for the user may besubsequently released and the user instead uses the CSR resources tosend scheduling requests. Upon a resumption of data activity, the DRXinactivity timer may be restarted and the periodic dedicated SRresources may be re-assigned to the user for the duration of the dataactivity (e.g. for the period of time that the DRX inactivity isrunning).

Conversely, in another example, a user may be assigned CSR resources forSR whilst a DRX inactivity timer is running and on expiry of the DRXinactivity timer (or at a time linked to the expiry of the DRXinactivity timer), the user instead uses DSR resources to sendscheduling requests. Upon a resumption of data activity, the DRXinactivity timer may be restarted and the user may revert to using theCSR resources. This approach may be used in order to provide a speciallow-latency scheduling request mechanism (using the common/shared SRresource) during periods of increased data activity, and which may beespecially suitable for traffic profiles such as on-line gaming, VoIP orother latency-sensitive applications.

Generally, it will be appreciated that the eNB may reserve one or moreportions of the PUCCH or PUSCH resources for common/shared use for aparticular group of UEs, and that these portions of resource aremultiplexed with other PUCCH or PUSCH resources, such as those used fordedicated SR on PUCCH. Switching of users between dedicated SR resourcesand common/shared SR resources may be governed by either:

-   -   i) explicit dedicated control signalling by the eNB (i.e.        commands sent from the eNB to the UE either allowing use of a        pre-defined common SR resource, or specifying the common SR        resources the UE should use)    -   ii) implicit mechanisms (i.e. a common/shared resource is        pre-defined and users switch between it and a user-dedicated SR        resource based upon triggering events commonly known to both the        eNB and the UE—such events may include the expiry of a timer        (such as an inactivity timer), a change in DRX pattern or a        change in a communication state, such as an RRC state, or        sub-state)

FIG. 23 and FIG. 24 show two examples of the explicit mode switchingmethod outlined in (i) above. In FIG. 23, the eNB pre-configures 2310one or more common/shared SR resources (e.g. via system informationbroadcast signalling or via user-dedicated signalling) and/or one ormore user-dedicated SR resources (e.g. via user-dedicated signalling).The pre-configuration may include for example, parameters specifying thetime, frequency, code or cyclic shifts of the SR resources. Based on adecision 2320 to switch the SR mode, the eNB controls which SR resourcesare in use by the UE via the sending of explicit SR mode-switch commands2330 to the UE. In an optional step, the UE may acknowledge 2340 the SRmode switch command 2330. The mode switch command 2330 and the modeswitch command acknowledgement 2340 may be sent at various layers of thecommunications stack, such as via RRC signalling (L3), MAC layersignalling (L2) or physical layer signalling (L1). On receipt of theexplicit mode switch command 2330, the UE transitions 2350 to use of thealternate SR resource. If more than two SR resources are specified inthe pre-configuration stage, these may each be associated with an indexand the SR mode switch command may then contain an index specifyingwhich SR resources the UE should use.

FIG. 24 shows a scheme which also uses explicit signalling to controlwhich SR resources are used by the UE. In contrast to FIG. 23 however,the step of pre-configuring 2310 the SR resources is omitted. Thus, inorder to change which SR resources are being used by the UE, the eNBsends an SR resource configuration 2430 via user-dedicated(point-to-point) signalling containing parameters that specify theparticular SR resources to use. The parameters may specify one or moreco-ordinates of the resource, such as time, frequency, code or cyclicshift resources. The UE may optionally acknowledge 2440 the SR resourcereconfiguration before transitioning 2450 to use the alternate SRresource.

FIG. 25 shows an implicit SR mode switching method corresponding to (ii)above. As in the first step of FIG. 23, the eNB pre-configures 2510 oneor more common/shared SR resources (e.g. via system informationbroadcast signalling or via user-dedicated signalling) and/or one ormore user-dedicated SR resources (e.g. via user-dedicated signalling).The pre-configuration may include for example, parameters specifying thetime, frequency, code or cyclic shifts of the SR resources. At asubsequent time, an event occurs 2520 that is commonly-known to both theUE and the eNB. Following the commonly-known event, and optionallyfollowing a known time delay, the UE transitions 2530 to use of one ofthe alternate (pre-configured) SR resources.

FIG. 23 and FIG. 24 show examples in which the eNB explicitly controlswhich SR mode is used and in which the decision to change SR mode ismade by the eNB. The decision at the eNB may be based on information ormeasurements either made directly by the eNB itself or based onmeasurements or information made by the UE and reported back to the eNB.Thus an SR mode decision function 2610 (such as that shown in FIG. 26)may exist in the eNB which takes information or measurements as a set ofinputs 2620, and generates an output 2630 relating to a preferred SRmode. The behaviour of the function may be further governed orcontrolled by SR mode ‘decision criteria information’ inputs 2640 whichmay be pre-programmed in the eNB, or which may be configured in the eNBvia an interface to another entity or network node, such as anoperations and maintenance (O&M) entity.

Alternatively, the UE may determine which SR mode is preferable and arecommendation may be sent to the eNB in order to request use of thepreferred SR mode. The eNB may be required to follow the request or maybe able to either allow or disallow the SR mode request. Thus an SR modedecision function 2610 may exist in the UE, again taking information ormeasurements as a set of inputs 2620, and generating an output 2630relating to a preferred SR mode.

FIG. 27 shows the case of a UE-initiated SR mode switch. Following apre-configuration of a plurality of SR resources 2710, an SR modedecision function 2610 located within the UE, determines 2720 that a newSR mode is appropriate therefore causing the UE to request a SR modechange 2730 and subsequently switching mode 2750 (optionally after thestep of receiving the instruction 2740 to change mode from the UE). Thebehaviour of the UE decision function 2610 may be governed or controlledby SR mode decision criteria inputs 2640 which may be pre-programmed inthe UE, or which may be configured in the UE by the eNB. Theconfiguration may be achieved via the eNB signalling parameters to theUE either via common (point-to-multipoint or broadcast) signalling (e.g.on system information) or via dedicated point-to-point signalling. Thesignalling may comprise RRC protocol messages and configuration datarelating to SR mode switching and associated criteria.

The system may therefore be augmented to include the ability to switchbetween use of the new contention-based SR mechanism and the originaldedicated SR mechanism based upon one or more factors input to an SRmode decision function 2610 located either within the eNB or within theUE. Inputs to the SR mode decision function may include:

-   -   A current data activity status or a data activity level of the        UE    -   A DRX state or sub-state, or change in the DRX pattern    -   Determination of whether one or more timers controlling DRX        behaviour are running or have expired    -   Determination of the activity of applications, services or        logical channels

Other inputs to the SR mode switch decision function 2610 are alsopossible. For example, noting that different applications or logicalchannels of the communication system are likely to have differing QoSand latency requirements, it may also be appropriate to switch SR modeas a function of data activity or inactivity of a particular logicalchannel, application or service. Thus, when a low-latency service orapplication becomes active or inactive, the SR resources used by the UEmay be adjusted accordingly. Similarly, the SR resources used by the UEmay be adjusted depending on whether a background application orlatency-tolerant service becomes active or inactive.

Additionally, switching between different SR resources may be based on apriority, such as a UE priority. For example, low priority users, orusers with low priority applications, may be assigned an SR resourcethat has a relatively high probability of collision, whereas highpriority users, or users with high priority applications, may beassigned an SR resource that has a lower probability of collision.

It may also be desirable to switch the SR mode, or SR resources used bya UE, as a function of prevailing radio channel conditions.

The proposed modification of the SR mechanism to carry a number ofexplicit UE bits (e.g. via PUCCH format 2 or format 3) does requireadditional transmission power at the UE to do so, when compared to theexisting PUCCH format 1 SR (which sends only 1 effective bit via on/offkeying). This affects both the coverage and capacity of the SR.

Overall system coverage may not however be significantly impacted by theproposed CSR technique. Whilst transmission of a user ID does requirethe sending of more bits (and so also more power) than a simple one-bitSR using on/off keying, the number of bits may be similar to thatrequired for other multi-bit UL control information types such aschannel status information (CQI/PMI/RI). That is, a UE located towardsthe edges of cell must in any case be capable of reliable UL controlinformation transfer for non-SR information types, and it is generallythese that set the coverage bound as they contain more bits than thesingle-bit SR. Additionally, a UE at the edges of cell must also be ableto communicate with the eNB via PUSCH according to a data ratecommensurate with a reasonable Service Level Agreement ‘SLA’ (forexample, a minimum supported UL data rate of 64 kbps or similar). Ifevery uplink sub-frame is utilised to meet this SLA this translates to64 bits per 1 ms TTI, again larger than the proposed small number of UEID bits for SR (e.g. up to 16 bits).

However, it is conceivable that some operators or network vendors wouldlike to retain the ability to operate an SR mechanism at the fringes ofcoverage that has a coverage performance equalling (or better than) thecurrent dedicated PUCCH format 1 SR scheme.

In recognition of these coverage aspects, the other factors that couldalso form the basis of SR mode-switching decisions include for example:

-   -   A determination or measurement of the pathloss between the eNB        and the UE    -   A determination or measurement of a downlink carrier to        interference (C/I) or downlink carrier to        interference-plus-noise (C/(N+I))    -   A determination or measurement of an uplink carrier to        interference (C/I) or uplink carrier to interference-plus-noise        (C/(N+I))    -   An uplink data rate for the UE    -   An uplink modulation and coding scheme for the UE    -   An uplink power headroom for the UE (e.g. a ratio of maximum UE        transmit power to a current UE transmit power)

The SR mode switching solutions proposed apply equally for CSR usingPUSCH based signal constructions.

Tx Diversity

Transmit diversity may be applied to CSR transmissions using PUCCHsignal constructions. Transmission diversity approaches can be brokendown into two categories: those that require modification to thestructure of a physical channel to support its transmission on multipleantennas (“non-transparent schemes”), and those that don't (“transparentschemes”). Both schemes have their advantages and disadvantages.

Since non-transparent schemes have more degrees of freedom in theirdesign, they typically provide better diversity gain than transparentschemes. However, the better diversity gain may have some costs. Themost obvious is additional system complexity, since differenttransmission and reception structures are used. Also, non-transparentschemes often require that the signals transmitted on each antenna bereceived independently, which typically requires that the channel toeach antenna be estimated independently. This leads to the use ofadditional reference signals (typically one set of reference signals perantenna). This use of additional reference signals can decrease spectralefficiency, since they may need to take up resource that could otherwiseconvey data, or be used to identify co-multiplexed UEs in the sameresource. Non-transparent schemes may also transmit redundantinformation on the antennas, which can further reduce spectralefficiency.

Transparent diversity schemes generally operate by transmittingtransformed copies of a physical channel on multiple antennas. Thetransformations are such that they could be caused by multipathpropagation of the channel, and so the receiver does not need todistinguish between single and multi-antenna transmission. Typicaltransformations include transmitting a copy of the physical channel onthe antennas with different delays, frequency offsets, or phase shifts.

One key property of the contention-based SR resource solutions here isthat they can be used with existing PUCCH formats. Multiple users cancontend on the same SR resource, using the same cyclic shift and/ororthogonal cover on both the data and reference symbols. We can use thisproperty to construct a transmit diversity scheme by allocating Ndifferent user IDs to a UE with N transmit antennas. The UE can transmitone PUCCH with a distinct ID on each antenna, and the eNB will receivethem in the same way as if they were contention-based PUCCH transmissionfrom multiple UEs.

Contention based transmission diversity can then be seen to haveproperties both in common and different from transparent andnon-transparent diversity. Each antenna will carry a signal withdifferent modulation symbols, which is similar to non-transparentschemes. However, unlike non-transparent schemes it does not requiremodification of the physical channel. Similar to transparent schemes, asingle reference signal can be used on each antenna, and the singleantenna receiver structure need not be modified to support diversitytransmission. Unlike transparent schemes, distinct information bitpayloads are associated with the different antennas.

A principal modification needed to support transmit diversity forcontention based SR is that the UE needs to be informed of theadditional IDs that it can use for diversity purposes. This could bedone by signalling each ID independently or by signalling a base ID andusing a fixed function to determine the remaining N IDs (such as addingpredetermined offsets to the base ID).

Once a UE knows which IDs it is to use, it can transmit using contentionbased TxD in a number of ways:

-   -   1. The UE can transmit N IDs simultaneously on a single        common/shared PUCCH resource with one distinct ID on each of the        N antennas. The eNB may use the decoded ID to determine which of        the UEs transmit antennas is currently the most reliable and        this information may be further exploited by the eNB during        subsequent communications with the UE. For example, the eNB        could use the information to instruct the UE to switch one or        more of its transmissions to the determined transmit antenna.    -   2. It can transmit one ID on one of the antennas. This antenna        selection may be done in an “open loop” or “closed loop” manner.        -   a. In an open loop approach, the selected antenna can be the            one that is estimated to have the most received power at            eNB. The UE can estimate the received power at eNB by            measuring the average downlink power from the eNB on each of            the UEs antennas, and assuming that the one with the most            average downlink power will have the most average uplink            power. In this case, the UE will be able to select the            antenna to transmit the ID on without feedback or control            from the eNB.        -   b. In a closed loop approach, the eNB can directly measure            the received power from each antenna and instruct the UE            which antenna to use to transmit contention-based PUCCH. In            this case, the eNB will need to be able to identify the            antennas the UE transmits on in order to provide the            feedback. Since the contention-based PUCCH TxD does not use            additional reference signals, some additional mechanism is            needed to identify the antennas.            -   i. One approach would be to associate the N IDs a UE has                with each of the N antennas, such that it transmits a                given ID only on a particular antenna port. When the UE                transmits a contention-based PUCCH, the eNB will                determine the received power, and associate it with the                UE's antenna port using the detected ID. The UE will                transmit on each of its antennas (using the associated                IDs) frequently enough for the eNB to select the proper                antenna given the rate of change of the channel. This                could be done by configuring the UE to periodically                transmit contention-based PUCCHs on at least two of its                antennas, or alternatively to transmit only on one                antenna at a time, but on different antennas in                different subframes (“hopping” over the antennas).            -   ii. A second approach uses information from existing                physical channels. When a Rel-10 UE is configured for                multi-antenna transmission, it will transmit physical                channels, including reference signals associated with                each antenna. In this case, the eNB can measure the                received power from each of the UE's antennas, and use                this to determine which antenna to select. For example,                if a UE is configured for two antenna port transmission                of PUCCH format 1b using Rel-10 LTE, it will have RS                associated with two antenna ports. In this case, the eNB                can select one of these two ports and instruct the UE to                use this for its contention based PUCCH transmissions.

Independent of whether open-loop or closed-loop diversity transmissionis used, the eNB can use a single receiver structure. The eNB willattempt to receive all IDs that can be transmitted from all UEs on allantennas in a given sub-frame and resource, and if it successfullydecodes any one of the N IDs assigned to a UE, it will determine thatthe UE has issued a scheduling request.

Alternatively, it is also possible to apply conventional open loop TxDtechniques to contention based SR. In this case, each UE transmits onlyone ID, although UEs transmitting simultaneously on a singlecommon/shared PUCCH resource will transmit using different IDs. Two TxDapproaches can be envisaged:

-   -   1. Non-transparent        -   a. The UE transmits distinct reference signals on each            antenna, enabling the eNB to estimate the channel to each            antenna independently. Two possible methods for            non-transparent TxD transmission of contention based SR are:            -   i. The UE may transmit using orthogonal resource                transmission diversity schemes, wherein a sequence of                modulated data symbols is replicated to each of the N                antennas, and each antenna transmits the sequence of                modulated data symbols on a contention based SR resource                that is different from the other antennas of the UE.                This method uses N contention SR resources, and so can                be spectrally inefficient. However, since each antenna                can be received independently, it provides full                diversity order and can require less transmit power than                more spectrally efficient schemes.            -   ii. Alternatively, the UE may transmit using block coded                transmit diversity, such as those based on so-called                Alamouti TxD schemes. In block coded TxD for contention                based SR, a sequence of modulated data symbols is broken                into symbol pairs, s1(i) and s2(j), where i=1, 2, . . .                , I and j=1, 2, . . . ,J and I+J is the total number of                modulation symbols in a single transmission of                contention based SR. Each antenna transmits on the same                contention based SR resource as the other antennas. For                two antenna block coded TxD, the first antenna will                transmit [s1(i), s2(i), s1(i+1), s2(i+1), . . . , s1(I),                s2(J)], and the second antenna will transmit [s2*(i),                −s1*(i), s2*(i+1), −s1*(i+1), . . . , s2*(I), −s1*(J)],                where * indicates complex conjugation of the modulation                symbol. This method can provide full diversity order,                and so can require low amounts of transmit power.                Furthermore, it uses one contention SR resource over all                antennas, and so can be spectrally efficient. However,                the spectral efficiency gains may not be available if                the multiplexing capacity is limited by the number of                available reference symbols. Also, receiver designs for                block coded TxD schemes tend to be more complex than for                orthogonal resource transmission schemes, and block TxD                schemes are more difficult to implement when there is                not an even number of modulation symbols to be                transmitted on a given set of space-time resources.    -   2. Transparent        -   a. The UE transmits the same reference symbols on each            antenna, transforming copies of the contention based SR            physical channel between antennas as described above with            reference to transparent diversity. The same advantages and            disadvantages apply as compared to non-transparent            approaches: it makes efficient use of contention based            resource, since only one resource is used for all antennas            (for both reference signals and modulated data symbols).            However, the full diversity order is generally not achieved,            so the performance with respect to required transmit power            is not as good as non-transparent schemes.            RRC Signalling Alternatives

In order to support the configuration of contention-based schedulingrequest (CSR) using PUCCH signal constructions, RRC signalling messagesor information elements could be modified to provide one or more of thefollowing:

-   -   i) to include an identifier indicating the PUCCH format type        (e.g. PUCCH format 1, 2 or 3) for the CSR resource.    -   ii) to specify a PUCCH resource index within an index range        (similar to the existing RRC parameters sr-PUCCH-ResourceIndex        and cqi-PUCCH-ResourceIndex for PUCCH formats 1 and 2        respectively). The index may identify a frequency and/or code        attribute of the common/shared SR resource. The index range        should be compatible with the specified PUCCH format type (e.g.        values 0-1185 for PUCCH format 2, or 0-549 for PUCCH format 3).    -   iii) to specify a PUSCH frequency resource or resource index.    -   iv) to specify a time-domain periodicity and sub-frame offset of        the CSR resource (e.g. similar to the existing RRC parameter        sr-ConfigIndex, but may be modified to provide an increased        number of possible resource periodicity values).    -   v) to include a field comprising a CSR-uRNTI to be used by the        UE in constructing signals to be transmitted on the CSR        resource. Alternatively, the field could comprise one or more        parameters that govern how the UE should determine the CSR-uRNTI        using its C-RNTI or another existing user ID. The CSR-uRNTI may        or may not be the same length as the 16-bit C-RNTI. If the        C-RNTI is directly used as the CSR-uRNTI, existing messages that        convey the C-RNTI to the UE are sufficient and there is no need        to signal a separate CSR-uRNTI.    -   vi) to include information describing how to map all or part of        a CSR-uRNTI or C-RNTI to sub-sets of time/frequency/code        resources within the indicated CSR resource. This may be used to        facilitate the case wherein some bits of a full user ID (e.g. a        C-RNTI or an ID derived there-from) are signalled explicitly by        the UE within the CSR signal transmission and the remaining bits        are signalled implicitly by the UE via CSR resource selection as        previously described.    -   vii) to include information which may be used to derive or set a        bit scrambling sequence or to disable bit scrambling. This may        be used to configure users accessing the same CSR resource to        use the same bit scrambling sequence for CSR transmissions (or        to use no bit scrambling). This information may include a field        containing a common or cell-specific RNTI or other scrambling ID        that is associated with the CSR resource in the cell and which        is to be used by the UE to initialise a scrambling sequence        generator (such as the generator shown in FIG. 16. Note that        this common or cell-specific scrambling ID could be the same as        (or related to) a group CSR RNTI (CSR-gRNTI).    -   viii) to include information which may be used to derive a        cyclic shift hopping pattern. This information may comprise a        value that is used to initialise a pseudo-random sequence        generator, the pseudo-random sequence being further used to        derive a cyclic shift hopping sequence. The value may be cell        specific, or may be a value that is associated with the CSR        resource being configured (such as a CSR-gRNTI).    -   ix) to include a parameter controlling how many consecutive        attempts the UE may make on the CSR resource before resorting to        other access methods.    -   x) to include a timer value controlling how long the UE should        wait (following a CSR transmission) for an UL grant addressed to        its C-RNTI before considering the transmission to have been        unsuccessful.

The information is carried from the eNB to the UE. For each of the aboveinformation fields, it may be possible to convey the particularinformation via dedicated (point-to-point) or common(point-to-multipoint) signalling means. Mixed approaches are possiblewherein some of the information is carried via dedicated signalling andsome via common signalling. Typically the information would be carriedvia RRC signalling messages or RRC information elements, but signallingof one or more of the above information fields is also possible at otherlayers including at the MAC layer or at the physical layer (e.g. viaPDCCH).

It should be appreciated that other forms of ASN construction are alsopossible and that examples are provided as examples only. Actual ASNconstruction may also vary according to the needs of backwardscompatibility with previous releases.

Particularly when the CSR resource is located within the PUSCH region,an alternative, is to allocate the resource using methods similar tothose used for semi-persistent scheduling (SPS) in LTE. In this case,dedicated RRC signalling (such as the RRC SPS-Config IE) could be usedto configure the same or partially overlapping SPS resource occasions intime to one or more UEs in the system and PDCCH messages could be usedto activate or deactivate the allocation, to specify the location infrequency of the CSR resource and possibly to convey other CSR resourceparameters.

In the same way as the existing uplink SPS mechanism, this RRCconfiguration signalling may also be used to provide each UE with anSPS-RNTI to which the UL grant messages (sent on PDCCH and relating tothe CSR resource) are addressed. This is termed here, an SPS-CSR-RNTI asit refers to a CSR resource assigned semi-persistently to the UE. TheSPS-CSR-RNTIs that are provided to the one or more UEs could be thesame, (for example, all could be equal to a CSR group RNTI “CSR-gRNTI”)which would enable group-based configuration, reconfiguration,activation or deactivation of the CSR resource and/or modification ofits associated parameters such as the frequency location of the RB(s).Alternatively, the SPS-CSR-RNTIs provided to each of the one or more UEsmay be different, in which case different PDCCH messages would need tobe sent to each UE in order to configure, reconfigure, activate ordeactivate the CSR resource. The SPS-CSR-RNTI could be signalled to theUE within the RRC SPS-Config IE simply by using the existing RRCparameter semiPersistSchedC-RNTI.

Whether achieved via dedicated RRC signalling or via dedicated PDCCHsignalling, the eNB may add or subtract UEs that have access to thecommon/shared SR resource in this manner.

If group-based addressing on PDCCH for CSR purposes is used, it may bebeneficial to configure parameters that define sub-frame occasions onwhich all UEs within the group should monitor PDCCH (e.g. addressed toSPS-CSR-RNTI=CSR-gRNTI) for possible CSR resource updates.

These common update occasions (known to both the eNB and to the group ofCSR UEs) may be specified in terms of a start sub-frame, a modificationperiod and a modification length. By using these parameters, a periodicPDCCH monitoring pattern may be defined in order to control on whichsub-frames the UE must check for CSR updates. These update occasions maytherefore lie within a ‘modification window’ which may recurperiodically.

PUSCH

As mentioned earlier, the CSR resource (conveying PUCCH-like SR signals)could reside in the PUSCH frequency region as well as or instead of thePUCCH frequency region.

FIG. 28 illustrates the steps for an alternative CSR scheme conveyingPUSCH-like SR (i.e. using PUSCH signal constructions). The PUSCH-like SRsignals may use either the PUSCH frequency region or the PUCCH frequencyregion for the CSR resources.

-   -   1) As a first step, an eNB optionally assigns 2810 a portion of        uplink resources (in either the control or data frequency        region) to a plurality of UEs for the purposes of        contention-based scheduling request. The resource assignment may        be conveyed via broadcast signalling or may be signalled        individually to each of the plurality of UEs. This first step        may be omitted if the resources are pre-defined, for example in        a standard.    -   2) At some later point, pending data arrives in the UEs        transmission buffer 2820    -   3) The UE encodes a user ID (or portion thereof) using a PUSCH        signal construction method, and transmits 2830 the signal on the        assigned CSR resource. Due to the fact that the payload carried        by PUSCH signals may be substantially larger than those carried        by PUCCH signals, there may be additional room within the        message to carry additional information fields. These may        comprise:        -   a. A buffer status report (BSR) indicating one or more data            volume levels within the UEs transmission buffer        -   b. A small amount of user data        -   c. Information related to current radio conditions    -   4) An eNB receiver attempts to decode 2840 signals from the CSR        resource, and if decoding of the UEs signal is successful, the        eNB subsequently derives the UE ID using the decoded        information. The eNB also decodes 2850 any additional        information fields (such as BSR, user data, or information        related to radio conditions) that the UE may have included    -   5) If the eNB determines that further PUSCH resources are        necessary, the eNB proceeds to send a normal UL-grant message        2860 to the UE to allocate it a portion of PUSCH resource for        the transmission of data. The eNB may take into account any        received BSR information or received information related to        radio conditions when determining how much PUSCH resource to        allocate to the UE and in determining formatting, modulation,        coding, or other attributes of the allocated PUSCH resource. The        UL-grant message is conveyed in a Downlink Control Format (DCI)        message sent over a Physical Downlink Control Channel (PDCCH).    -   6) The UE then has access 2870 to further PUSCH and is able to        send (further) data to the eNB.

One particular implementation of step 2830 above is to send the user'sC-RNTI within a MAC C-RNTI Control Element. By doing so, the schemereuses existing building blocks of the LTE system thereby improving itscompatibility with existing systems and minimising the need foradditional modifications to support the invention.

Information Fields within CSR-PUSCH Transmissions

The C-RNTI MAC CE is originally only used during the RACH procedure,therefore in some embodiments, the C-RNTI MAC CE is reused for thepurposes of contention-based scheduling request on PUSCH.

In addition to a C-RNTI MAC CE, a PUSCH transmission on a CSR resourcemay contain (for example, within a MAC transport block 300 or a MACpayload 320) a number of other data elements like a Buffer Status Report(BSR) (for example within a MAC CE 330), User data (MAC SDUs) 340 andMAC Padding bits 350. The BSR may be a Long BSR (L-BSR) or a Short BSR(S-BSR).

FIG. 29 shows some example MAC PDU constructions (2901 to 2912) for CSRtransmissions. The C-RNTI MAC CE is necessary in all cases in order toallow the eNB to identify the user. Cases 2902 to 2908 show theinclusion of other fields along with the necessary MAC subheaders(denoted “Sub-H” in the figure). The C-RNTI CE and BSR CE MAC subheadersare each of length 1 byte. The subheaders for a MAC SDU or for paddingare normally 2 bytes, but are length 1 byte when they are the lastsubheader in the MAC PDU.

The network may wish to control whether or not the various fields may beincluded by the UE(s) within PUSCH transmissions on the CSR resource. Inparticular the eNB may wish to control whether or not UEs may send userdata on the CSR resource:

-   -   “Data Allowed”: In this mode, the UE sends a C-RNTI MAC CE and        may also send user data within MAC SDUs and optionally also        append a BSR MAC CE. This mode is used for transmission of        (small) amounts of user data piggybacked on to the CSR        transmission. This may improve the latency of the data transfer        and may increase the efficiency of usage of the CSR PUSCH        resource in general. This may be especially useful for sending        small amounts of TCP or other higher layer control data such as        acknowledgements or keep-alives and PINGs. Typical sizes of        these data packets may be approximately 40-60 bytes.    -   “Data NOT Allowed”: In this mode, the UE transmits only the        C-RNTI MAC CE and optionally a BSR MAC CE. This mode is used by        the UE to make a scheduling request on the CSR-PUSCH resources.

UE and network procedures may differ significantly depending on whetheruser data is carried within a CSR PUSCH transmission. For example, HARQmay be operated if user data is carried, whereas this may not benecessary if user data is not carried.

Two possibilities exist to provide the eNB with the ability to controlwhether or not data is allowed. In a first option, the eNB may sendexplicit commands within UE dedicated or common/broadcast RRC signallingmessages. In a second option, the eNB may control whether user data maybe sent via the establishment of information field priority rules and byadjusting the size and Modulation and Coding Scheme (MCS) of the grantedCSR resource. This second option will be further described in thefollowing.

Within the LTE system, the UE returns a MAC PDU with a transport blocksize (TBS) commensurate with the allocated number of PRBs and theassigned MCS. Therefore, if rules are established governing whichinformation types are to be prioritised within a CSR transmission, theeNB may control which information types are actually included by meansof adjusting the assigned TBS (i.e. via the assigned number of PRBs andthe assigned MCS). In this way, the eNB does not need to explicitlysignal a separate field to allow or disallow data transmission or toenable/disable the transmission of different MAC control elements.

By means of example, the eNB may configure 1 RB of CSR resource alongwith an MCS that supports the transmission of a number (denoted TBS) ofbits. Transmission of the various possible information fields may thenbe prioritised (in decreasing priority order) as follows:

-   -   {C-RNTI MAC CE, BSR MAC CE, user data in MAC SDUs}

Thus, the value of TBS may be used to control which information fieldsare included by the UE within its CSR transmissions, e.g.

-   -   An assignment of an MCS supporting only 24 bits (3 bytes) may be        interpreted by the UE as an instruction to send only its C-RNTI        MAC CE—(see 2901)    -   An MCS assignment of 40 bits (5 bytes) may be interpreted as an        instruction to send the C-RNTI MAC CE along with a short        BSR—(see 2905)    -   An MCS assignment of 56 (7 bytes) bits may be interpreted as an        instruction to send the C-RNTI MAC CE along with a long BSR—        (see 2909)    -   An MCS assignment of >T bytes may be interpreted as an allowance        to send user data within MAC SDUs (along with the accompanying        C-RNTI MAC CE and a long BSR). The value of T may be fixed (e.g.        T=8 bytes) or may be a variable value and signalled to the UE.

For the case in which no data or padding is transmitted on the CSRresource, the MAC PDU size may comprise up to 56 bits (7 bytes). Thephysical layer then adds a 24 bit CRC to the transport block. Thus atotal of 80 bits of data may need to be encoded by the turbo encoder inorder to form the eventual PUSCH CSR signal. One PUSCH RB carries up to144 REs of data and assuming QPSK modulation, this accommodates up to288 coded bits of data. Hence, a code rate of around ⅕th is possible.Thus a scheduling request containing both a C-RNTI and a long BSR fitseasily into one RB using a robust modulation format and with a low coderate, thereby helping to ensure its reliable transmission.

For the case in which user data is allowed, one further option could beto allow the mobile to send small amounts of user data only if theentire UE buffer contents may be sent within a single transmission onthe CSR-PUSCH resource. In this case the BSR need not be included in theMAC header (eg 2902). Instead the network will interpret a CSRtransmission containing user data but no BSR MAC CE as an indicationthat the UEs buffer is now empty. Hence on successful reception of thismessage the eNB will not allocate any additional dedicated PUSCHresources to the UE.

Alternatively, the UE may transmit a small amount of data on theCSR-PUSCH resource even though this represents only a portion of thedata in the UEs transmit buffer. In this case the mobile includes theBSR in addition to the data transmitted (see 2906 and 2910).

For typical small user data messages (e.g. 40 bytes and more), theoverall MAC PDU payload rises to >344 bits and hence no longer fitswithin one RB using QPSK modulation (a maximum TBS of 144 bits issupported for QPSK on PUSCH within 1 RB). Hence either a higher ordermodulation scheme or a higher number of RBs for the CSR resource will beneeded to send typically-sized small data messages in full.

Alternatively, and if allowed by the network, only a portion of the UEbuffer may be sent within the initial CSR PUSCH transmission, along witha BSR, and the remainder of the buffer may be sent in one or moresubsequent PUSCH transmissions (i.e. on PUSCH resources assigned to theUEs C-RNTI)

Inclusion of Radio Channel Status Information

In addition to transmission of a user ID and optionally a buffer statusreport, it may be beneficial to also include information regardingpresent radio channel conditions within a CSR-PUSCH transmission. Thismay be used by the eNB scheduler to allocate to the UE an appropriateamount or type of resource and to assign an appropriate MCS or transmitpower for subsequent transmissions. Such functionality is not possiblewith existing scheduling request mechanisms that do not conveyinformation regarding present radio channel conditions.

The radio channel condition information reported by the UE may includeone or more of:

-   -   A Channel Quality Information (CQI) report        -   Information related to the downlink quality and which may be            used by the eNB to determine an appropriate MCS to use for            downlink (or optionally also uplink) transmissions    -   A Precoding Matrix Indication (PMI) report        -   Information related to the downlink quality and indicating            an appropriate precoding to use for downlink transmissions    -   A Rank Indication (RI) report        -   Information related to the downlink quality and indicating            an appropriate rank (spatial multiplexing order) to use for            downlink transmissions    -   A Channel Status Information (CSI) report        -   Information regarding the received quality of one or more            cells    -   A Power Headroom Report (PHR)        -   Information indicating a difference between a maximum UE            output power level and a current estimated UE power for            PUSCH transmission

The radio channel condition information may be multiplexed with otherinformation carried on PUSCH in one of two ways:

-   -   1) Via physical layer multiplexing: the radio channel condition        information is used to construct uplink control information        (UCI) which may be encoded separately from other data carried on        PUSCH, and which may be mapped to particular resource elements        of the PUSCH transmission    -   2) Via MAC multiplexing: the radio channel condition information        may be contained within MAC control elements that are        multiplexed with other MAC control elements and/or MAC data        PDUs. For example, a power headroom MAC control element may be        included within a CSR-PUSCH transmission.

Mixtures of (1) and (2) above are also possible. For example, aCSR-PUSCH transmission could carry CQI/PMI within uplink controlinformation that is multiplexed at the physical layer (1), and couldalso carry a power headroom report within a MAC control element andwhich is multiplexed at the MAC layer (2).

The Network may wish to control whether or not UEs should include theinformation related to radio conditions within PUSCH transmissions on aCSR resource. This may be achieved via the transmission of relatedconfiguration information from the eNB to the UE via dedicated or commonsignalling methods, for example using RRC, MAC or Physical Layersignalling.

Allocation of CSR-PUSCH Resources

Semi-Static allocation. The location of the CSR-PUSCH resources could besemi-static and may be signalled within dedicated RRC messages to aparticular UE, or within one of the broadcast messages in a SystemInformation Broadcast (SIB) frame.

A new information element (IE) (CSR-PUSCH-Config) could be created tocarry both the time domain CSR-PUSCH pattern and the Resource Blocks andMCS used for CSR-PUSCH thereby providing a fully semi-static RRCconfiguration and obviating the need for PDCCH assignments for CSR.

The CSR frequency resources may be specified within the RRC IE by aparameter csr-RIV. The principle used employs a Resource IndicationValue (RIV) which corresponds to both a start RB and a length ofcontiguously-allocated virtual resource blocks and is adopted from themechanism used to allocate PUSCH via DCI format 0 on PDCCH. The numberof possible RIV values is a function of the number of UL RBs within thesystem bandwidth (N_(RB) ^(UL)). A smaller range of RIV values (and adifferent mapping of RIV to the location and number of allocated PRBs)may be used if the number or location of the PRBs for CSR-PUSCH isrestricted.

The IE may also include other necessary fields usually found in DCIformat 0 and which specify an MCS for the CSR resource (e.g. 5 bits),and a demodulation reference signal (DM RS) cyclic shift to use (e.g. 3bits). Either of these fields may be omitted from the IE if a fixed MCSor fixed DM RS cyclic shift are used for CSR.

A CSR-gRNTI is optionally also included within the IE to enable all UEswithin a cell to use a common bit scrambling sequence when transmittingon the configured CSR-PUSCH resource.

The network may increase or decrease the number of available CSR-PUSCHresource blocks in the system based on the determined system load orbased upon a determined collision probability, or based upon adetermined CSR access latency.

More than one assignment of CSR-PUSCH resources may be reserved in thesystem and specific rules governing the usage of a given CSR resource bya given UE may also be signalled in a StstemInformationBlockType2 (SIB2)message or within dedicated RRC signalling messages. For instance, theCSR-PUSCH resources may be designated to have varying degrees ofpriority and certain CSR-PUSCH resources may be reserved only forcertain UEs (the priority level of a given UE being signalled to the UEduring the RRC connection set-up).

Hybrid/SPS-like allocation of CSR-PUSCH resources. Semi-PersistentScheduling (SPS) may be used in LTE to assign periodically recurringPUSCH resources for the transmission of regular uplink data. CSR PUSCHresources may be allocated using SPS-like principles, that is, by usinga combination of RRC signalling (to specify the time-domain occurrencesof the resource) and using PDCCH to activate or deactivate theassignment, and to configure or reconfigure its parameters (such as itsfrequency resources and MCS). The PDCCH transmissions may be addressedto an individual UE (using a C-RNTI address) or to a group of UEs (forexample using a common CSR-gRNTI address allocated to the group of UEs).

If group-based addressing is used (CSR-gRNTI on PDCCH), it may bebeneficial to configure parameters that define sub-frame occasions onwhich all UEs within the group should monitor PDCCH for possible CSRresource updates.

These common update occasions (known to both the eNB and to the group ofCSR UEs) may be specified in terms of a start sub-frame, a modificationperiod and a modification length. By using these parameters, a periodicPDCCH monitoring pattern may be defined in order to control on whichsubframes the UE must check for CSR updates. These update occasions maytherefore lie within a ‘modification window’ which may recurperiodically. For example, a rule may be defined that UEs should monitorall sub-frames for which the following equation is TRUE:((SFN*10+n+modification_offset)mod(modification_period))<(modification_length)where:

-   -   SFN is the System Frame Number    -   n is the current subframe (0-9) within the frame    -   modification_offset is the subframe offset parameter    -   modification_period and modification_length are expressed in        durations of subframes

In the equation, SFN is the System Frame Number, n is the currentsubframe (0-9) within the frame, modification_offset is the subframeoffset parameter, and modification_period and modification_length areexpressed in durations of subframes.

As an illustrative example, if the offset parameter was set to 0,modification_period was set to 500, and the modification length was setto 10, UEs would check for PDCCH modifications to the CSR resource (e.g.with the PDCCHs addressed to CSR-gRNTI) on the subframes: {[0, 1, . . .9], [500, 501, . . . , 509], [1000, 1001, . . . 1009], [1500, 1501, . .. , 1509], . . . } and so on.

Dynamic allocation. In a dynamic allocation method, CSR allocations maybe made via PDCCH. In order to support the dynamic allocation approach,the group of UEs which are allowed to transmit on the CSR-PUSCHresources may be allocated a common CSR-gRNTI at the RRC connectionsetup procedure or alternatively the g-RNTI may be configured via SystemInformation on the broadcast channel.

The CSR-gRNTI for the UE may be signalled to the UE during the RRCconnection setup phase (for instance by defining a new element in theradioResourceConfigDedicated IE).

The actual CSR-PUSCH resources will then be allocated dynamically (eg:on a per sub-frame basis) using DCI format 0 UL grants within PDCCHtransmissions addressed to the CSR-gCRNTI. All the UEs sharing theCSR-gCRNTI will then be allowed to send CSR-PUSCH transmissions on theindicated resource.

Whilst dynamic allocation of the CSR-PUSCH resources using the PDCCHgives the network a higher degree of flexibility in assigning theCSR-PUSCH resources, it also consumes more resources on the PDCCH in thedownlink compared to a semi-static or a hybrid/SPS-like method ofallocating CSR-PUSCH resource.

MCS and Link Control

Modulation order control. Controlling the modulation order and/ortransmit power at the UE may be important to guarantee essential qualityof service on the CSR-PUSCH resources. A group of users may beconfigured to use the CSR resource and for reasons of eNB simplicity, itmay be preferable for the users to employ a common MCS for theirtransmissions. The use of different MCS per user is possible but entailssignificant complications for the eNB receiver design as it has to thenperform blind decoding attempts for all possible MCS in order to decodethe user transmissions.

If employing small MAC PDU sizes (e.g. Data NOT Allowed mode) on theCSR-PUSCH resources, one strategy would be simply to use QPSK modulationand a transport block size sufficient to carry a C-RNTI MAC CE alongwith a BSR. Such a message fits well within one QPSK RB and offers ahigh degree of FEC protection. In this case, it could be specified thata fixed CSR-PUSCH size of 1 PRB is used and/or a fixed MCS for CSR-PUSCHtransmissions is used, thereby avoiding the need for any signalling toconfigure one or both of these parameters. This could mean that thecsr-MCS parameter could be omitted from the CSR-PUSCH-Config IE and thatthe csr-RIV field in the same IE could be simplified (due to the need toonly support a fixed size PRB allocation). Alternatively, the number ofPRBs and/or the MCS may remain flexible and signalled by the network.

In the case of Data Allowed mode on CSR-PUSCH resources, largertransport block sizes could be configured, either by providing a largernumber of resource blocks or by utilising higher MCS.

Once an initial MCS and PRB allocation size have been configured, thesemay remain fixed for a long period of time, or the network could varythem on a more dynamic basis. In the latter case, the signallingmechanism used to vary the MCS would typically be the same as that usedto initially configure the MCS (RRC signalling or PDCCH). Due to theneed for all users of the CSR group to be able to reliably communicatevia the CSR resource to the eNB, it may be desirable to consider theradio conditions of the group of UEs before changing the MCS.

Power control. Users transmitting scheduling requests are those withoutimmediate access to normal PUSCH resources. Hence these users may beless likely to have converged closed-loop power control loops for PUSCH.

3GPP Technical Specification (TS) 36.213 contains a description ofuplink power control procedures. Whilst normal PUSCH power controlprocedures may be followed, an alternative is to employ open loop powercontrol for transmissions on the CSR-PUSCH resources. This may beachieved for example by setting a TPC accumulation value f(i)=0 for CSRtransmissions.

One possible further enhancement is that a separate open loop powercontrol offset value (P_(O) _(—) _(PUSCH)) or another offset value maybe used specifically for CSR transmissions. Offset values specific toCSR transmissions may be fixed values or may be configured by the eNBvia common or dedicated RRC signalling.

Aspects of synchronisation. Only UEs that are synchronised (i.e theirTiming Alignment Timers (TAT) are running) are allowed to access theCSR-PUSCH or CSR-PUCCH resources and if the UEs are not synchronisedthey need to request access to PUSCH resources via the RACH procedure.The network may attempt to periodically refresh the timing advance ofthe UEs in CSR-PUSCH or CSR-PUCCH mode to keep them synchronised.Typically slow moving UEs are more suitable for using the CSR-PUSCH orCSR-PUCCH based procedures described above. Also cells covering smallgeographical areas will be more suitable due to the fact that the timedelays associated with radio propagation over smaller cell radiidistances may continue to lie within the SC-FDMA cyclic prefix length.

For messages transmitted without user data (e.g. those sent in Data NOTAllowed mode) these may be sent on CSR-PUSCH without using HARQ. In thiscase, a Physical Hybrid ARQ Indicator Channel (PHICH) may not be usedfor CSR-related purposes (although implementations that do make use ofPHICH for CSR ACK/NACK feedback purposes are possible). Without usingPHICH, the eNB is able to acknowledge any successful receipt of aCSR-PUSCH transmission by sending an uplink grant to the UE via PDCCHaddressed to the successful UEs C-RNTI (the uplink grant also assignsany available PUSCH resources to the UE). The UE may interpret theabsence of such an UL grant as an indication that its CSR-PUSCHtransmission was not successfully decoded by the eNB (or that no ULPUSCH resources were available to the eNB to grant at this time). Inthis case, the UE may reattempt a CSR-PUSCH transmission (for apredetermined number of attempts) at a later time (possibly following apredetermined or random backoff time) or may revert to other SR accessmethods (e.g. RACH or DSR).

An example UE procedure for retransmission is depicted in FIG. 30. Thefigure includes cases where, for messages with user data (e.g. thosesent in Data Allowed mode) HARQ may or may not be applied: An RRC IEsuch as a CSR-PUSCH-Config IE may be sent by the eNB to the UE in orderto configure aspects of the desired CSR-PUSCH procedure.

If HARQ is applied 3005, the PHICH is used to return ACK/NACKinformation 3010 to the UE and to implicitly (re)schedule the same ULresources for the subsequent retransmission 3060.

-   -   For synchronous HARQ, the ACK/NACK information on the PHICH        channel occurs at a predetermined point in time after the        transmission of the data (eg: 4 sub-frames later in case of FDD        system) and any retransmissions (by the UE) after the ACK/NACK        reception would also occur at a predetermined point in time        after reception of the ACK/NACK information on the PHICH. The        retransmissions may or may not coincide with the CSR ‘initial        transmission’ resources depending on the particular scheduling        pattern of the CSR resource and on the HARQ round trip time. The        number of HARQ retransmissions (i.e. retransmissions triggered        as a result of receiving a NACK on the corresponding PHICH) may        be limited by signalling a csr-maxHARQ-Tx field 3020 within the        CSR-PUSCH-Config IE.    -   The presence of an ACK on the PHICH resource 3015 corresponding        to the CSR-PUSCH transmission only gives the UE an early        indication that its transmission may have been successful.        However, if more than one UE transmits on the CSR-PUSCH        resource, the ACK on the PHICH cannot distinguish between the        UEs. Hence, even after seeing an ACK on the PHICH resource, the        UE needs to further wait 3030 for another mechanism to resolve        the actual UE ID to which the ACK was addressed. One way to        achieve this resolution of UE ID (contention resolution) is to        wait for a grant (for up to a given number of sub-frames eg: as        signalled in a csr-ResponseTimer field within the        CSR-PUSCH-Config IE).    -   If the UE doesn't receive a grant or an ACK/NACK then the UE may        try to retransmit 3035 on the CSR-PUSCH resources for up to a        given number of times (eg: as signalled in a csr-TransMax field        3040 within the CSR-PUSCH-Config IE) before resorting to other        SR mechanisms (eg: RACH based SR) 3050.    -   If the UE has no further data to send after transmitting the        data on the CSR-PUSCH resource, the UE may ignore the grant. It        should be noted that the network may be made aware of this        scenario (e.g: the UE may indicate this to the eNB by including        a BSR indicating no further data or by an implicit means such as        including no BSR).    -   The eNB may combine any HARQ retransmission with the previous        transmission before again attempting to decode the message.

If HARQ is not applied 3025, the PHICH need not be used for CSR-relatedpurposes. As described above for the case of CSR without user data, theeNB is able to acknowledge any successful receipt of a CSR PUSCHtransmission by sending an uplink grant to the UE via PDCCH addressed tothe successful UEs C-RNTI. On the absence of such an UL grant, the UEmay retransmit the data to the eNB during another CSR resource occasion,but the eNB would typically not attempt to combine the retransmissionwith the previous transmission prior to decoding.

DRX Interactions

A UE which is either in a long or a short DRX cycle and for which newdata arrives in the UE buffer, may act according the following:

-   -   In the case of static or semi-static allocation of CSR-PUSCH        resources: the UE may transmit any CSR-PUSCH messages that have        been generated on the allocated CSR-PUSCH resources.    -   In the case of SPS-like allocation of CSR-PUSCH: The UE may        first check that the SPS-CSR-PUSCH allocation will still be        valid for the next occurrence of the SPS-CSR-PUSCH resource. The        determination may be based upon the system frame number and        sub-frame number of the next occurrence of the resource and may        further be based upon whether the UE receiver actively monitored        for CSR resource configuration updates (on PDCCH addressed to        CSR-gRNTI) within a previous modification window. Additionally,        if a new modification window is due to start before the        occurrence of the CSR resource, the UE may also check the        intervening sub-frames for possible CSR resource configuration        updates.        -   On the arrival of the upcoming CSR resource occurrence, the            UE may transmit CSR on that occurrence only if the UE has            determined that the allocation is valid.        -   If the UE determined that the resource occurrence was not            valid, the UE may either use an alternative method to send            SR (e.g. RACH or DSR if allowed to do so by the eNB) or            continue to monitor PDCCH during the CSR modification            windows in order to identify valid resource occasions.    -   Note that it may be beneficial to configure the modification        windows to align with (or to be a sub-set of) the UEs DRX cycle        on-durations, thereby ensuring that the UE is able to read the        CSR resource update messages on PDCCH as a natural part of its        existing DRX behaviour.    -   In the case of Dynamic allocation of CSR-PUSCH resources: the UE        shall read the PDCCH for a period of time to check whether a        grant for the CSR-gCRNTI is made available by the eNB and, if        so, access the CSR-PUSCH resources. If a CSR-PUSCH allocation is        not detected within the period of time, the UE may revert to the        use of other SR mechanisms (such as RACH or DSR) if allowed to        do so by the eNB. The period of time may be a fixed value or a        configurable parameter that may be signalled by the eNB to the        UE, e.g. via RRC signalling.

If the UE accesses the CSR-PUSCH resources according to any of the aboverules, upon transmission of on the CSR resource, it shall come out ofDRX (by restarting the DRX Inactivity Timer) and will listen on one ormore subsequent sub-frames for a grant on PDCCH.

If HARQ is enabled, the UE may also check PHICH for an acknowledgementof the data (e.g. in the case of the Data Allowed mode of operation).

PUSCH Scrambling

The data sent on PUSCH resources are scrambled prior to modulation.According to the current specifications (section 5.3.1 of 3GPP TS36.211), the scrambling sequence is created by a generator that isinitialised at the start of each sub-frame as a function of threevariables:

-   -   i) the cell ID    -   ii) an “nRNTI” value (the RNTI associated with the PUSCH        transmission (e.g. C-RNTI or SPS-RNTI))    -   iii) the slot/sub-frame number within the radio frame.

The function is shown below in which c_(init) is the initialisationvalue for the scrambling code generator, N_(ID) ^(cell) is the cell IDand n_(s) is the slot number in the radio frame (0 . . . 19).c _(init) =n _(RNTI)·2¹⁴ +└n _(s)/2┘·2⁹ +N _(ID) ^(cell)

In the case of CSR PUSCH resources, the network is unaware of theparticular UE transmitting on the resources and so in order to reduceeNB receiver complexity, a common scrambling code is preferred for thegroup of UEs sharing the CSR-PUSCH resource. This can be achieved by:

-   -   1) using only the cell ID and/or the slot/sub-frame number to        initialise the scrambling sequence (if the above formula was        continued to be used, this would be equivalent to setting the        nRNTI value equal to zero)    -   2) setting nRNTI equal to a fixed or known value for all UEs        with access to the same CSR-PUSCH resource. For example, nRNTI        could be set equal to the CSR-gRNTI

Alternatively, the bit scrambling function could be disabled entirelyfor CSR-PUSCH transmissions (equivalent to scrambling with an all-zerosbit sequence).

Collision Aspects

In the case of normal PUSCH transmissions, the cyclic shift fordemodulation reference signal (DMRS) is signalled in the downlink PDCCH(using DCI format 0). This may be used by the eNB to implement uplinkMulti-User MIMO (MU-MIMO), wherein the eNB may schedule (andsuccessfully receive) multiple users simultaneously on the same PUSCHresource. By ensuring that each user uses a different cyclic shift, thereceiver may be able to more accurately estimate the individual channelresponses for each of the users.

In the case of CSR-PUSCH the eNB is not in control of exactly whichusers will transmit on a given instance of the CSR PUSCH resource. Ifthe eNB wishes to exploit the potential for different transmitting usersto have different cyclic shifts (e.g. possibly to implement MU-MIMO onthe CSR-PUSCH resource), the eNB may allow the UEs to pick the cyclicshift at random from within either the full range of possible cyclicshifts, or within a restricted range of shifts. Alternatively, if theeNB wishes for users to use the same cyclic shifts for their referencesignals, the eNB may define a particular cyclic shift for the UEs touse. In either case, the cyclic shift configuration may be signalled viathe RRC signalling messages for the CSR-PUSCH resource allocation). IfCSR-PUSCH is dynamically allocated, or allocated using SPS-like methods,a further alternative is for the cyclic shift configuration to besignalled via DCI format messages on PDCCH.

Benefits

There are a number of benefits of the proposed solutions, a few of whichare listed below:

Use of a common or shared resource for scheduling request is able toprovide significantly increased resource efficiency when compared to theexisting dedicated scheduling request scheme. This is especially true inthe case of large connected mode user populations comprisingcommunication devices that may transmit small amounts of traffic on arelatively infrequent basis. Such traffic may for example be generatedby background applications or a diversity of other data applicationsrunning on smartphone or tablet devices.

The scheduling request schemes are able to offer significantly loweraccess latencies when compared to the existing dedicated schedulingrequest scheme, and this is again especially true in the case of largeconnected mode user populations such as described above.

The schemes offer alternative contention-based scheduling requestmechanisms to the existing RACH procedure. When compared to theRACH-based method, the signalling overheads and the total number ofexchanged signalling messages may be reduced during access attempts viause of the proposed contention-based scheduling request scheme.Additionally the resource of the proposed CSR schemes may be moreefficient the existing RACH procedure.

By utilising multi-bit user IDs (e.g. 8-16-bits) within the CSRtransmission, the system is able to assign a large number of users tothe same CSR resource. This is able to significantly increase the usageefficiency (occupancy) of the assigned resource, even when theprobability of CSR transmission by any one user remains low.

The schemes can be designed to be backwards compatible with existingPUCCH and/or PUSCH transmissions (e.g. with dedicated SR and CQI/PMI/RItransmissions on PUCCH, or data transmissions on PUSCH).

The schemes can be designed to be largely backwards compatible withexisting physical layer and MAC designs in both the eNB and the UE.

The schemes may allow for improved user-ID detection performance incollision scenarios where multiple users simultaneously access the sameresource.

The PUSCH scheme allows for the transmission of additional buffer statusinformation and/or radio condition information within an initialscheduling request message, thereby enabling the eNB to rapidly assignan appropriate amount and type of uplink resource to the UE.

The invention claimed is:
 1. A method implemented in a user equipment UEfor use in a wireless system for single carrier frequency divisionmultiple access SC-FDMA, the method comprising: receiving an assignmentof a recurring scheduling request resource in the wireless systemcomprising a plurality of subcarriers, wherein the recurring schedulingrequest resource is assigned to a plurality of UEs; encoding a user ID;and transmitting an SC-FDMA uplink control channel signal comprising theencoded user ID on the plurality of subcarriers of the assignedscheduling request resource.
 2. A method according to claim 1 furthercomprising: determining a need to transmit on scheduled uplink resourcesin the SC-FDMA wireless system; and wherein said transmitting isperformed upon determining the need to transmit on scheduled uplinkresources.
 3. A method according to claim 1 wherein encoding the user IDcomprises generating encoded bits and the method further comprises:modulating the encoded bits to produce modulated symbols; spreading themodulated symbols; and mapping each of the spread modulated symbols tothe plurality of subcarriers.
 4. A method according to claim 1 whereinthe assignment is received from a broadcast transmission or commonsignalling message transmitted by an eNB of the wireless system.
 5. Amethod according to claim 1 wherein said assignment is received from adedicated transmission to the UE by an eNB of the wireless system.
 6. Amethod according to claim 1 wherein the user ID is related to a CellRadio Network Temporary Identifier C-RNTI.
 7. A method according toclaim 1 wherein the step of encoding comprises using a block forwarderror correction FEC encoder.
 8. A method according to claim 1 whereinthe SC-FDMA uplink control channel signal comprises a Physical UplinkControl Channel PUCCH format 2 or format 3 signal.
 9. A method accordingto claim 8 further comprising selecting a constituent resource from theplurality of constituent resources and transmitting the SC-FDMA uplinkcontrol channel signal on the selected constituent resource.
 10. Amethod according to claim 9 wherein encoding the user ID comprisesencoding a first portion of the user ID and wherein selecting theconstituent resource from within the plurality of constituent resourcesis based upon a second portion of the user ID.
 11. A method according toclaim 1 wherein the scheduling request resource comprises a plurality ofconstituent scheduling request resources.
 12. A method according toclaim 11 wherein transmitting the SC-FDMA uplink control channel signalcomprising the encoded user ID comprises making a plurality oftransmissions on the plurality of the constituent resources.
 13. Amethod according to claim 1 wherein the user ID is encoded using anon-user-specific bit scrambling sequence associated with the sharedassigned scheduling request resource.
 14. A method according to claim 13wherein information related to construct the non-user-specific bitscrambling sequence is received from an eNB of the wireless system. 15.A method according to claim 1 wherein the assigned SC-FDMA schedulingrequest resource is within a PUCCH frequency region of an uplink systembandwidth of the wireless system.
 16. A method according to claim 1wherein the assigned SC-FDMA scheduling request resource is within aPUSCH frequency region of an uplink system bandwidth of the wirelesssystem.
 17. A method according to claim 1 further comprising calculatingand appending a cyclic redundancy check code CRC to the transmission.18. A method according to claim 17 further wherein the CRC is calculatedand appended to the user ID prior to encoding the user ID.
 19. A methodaccording to claim 1 wherein said UE comprises a plurality of antennasand has a plurality of associated user IDs, the method furthercomprising: associating an antenna with one of the user IDs; whereinencoding the user ID comprises encoding the user ID associated with theantenna; and transmitting the encoded user ID is performed using atleast the antenna associated with the user ID.
 20. A method according toclaim 19 further comprising selecting an antenna for transmission,wherein the UE determines the selected antenna for transmission bymeasuring signals transmitted from an access node on the plurality ofantennas.
 21. A method according to claim 19 further comprisingselecting an antenna for transmission in response to receiving aninstruction from an access node as to which of the plurality of antennasto select.
 22. A method according to claim 21 comprising associatingeach of the plurality of user IDs with a particular antenna such that areceiving access node can measure a received power from a transmissionof the user ID by the UE and associate it with the UE's antenna usingthe received user ID.
 23. A method according to claim 22 wherein thetransmitted signal comprises reference signals associated with eachantenna such that the eNB can measure a received power from each of theUE's antennas and use the measured power to generate the instruction fortransmission to the UE.
 24. A method according to claim 1 wherein saidUE comprises multiple antennas each associated with a particular userID, the method further comprising encoding each of the plurality of userIDs and transmitting the encoded user IDs from their respectiveassociated antennas simultaneously on the assigned scheduling requestresource.
 25. A method according to claim 1 wherein a plurality ofantennas are associated with one user ID.
 26. A method according toclaim 25 further comprising transmitting a plurality of distinctreference signals, wherein each of the distinct reference signals istransmitted on one of the plurality of antennas associated with the oneuser ID.
 27. A method according to claim 1 wherein said assignedresource is associated with a first scheduling request resource type,and said method further comprises: receiving a further assigned resourceassociated with a second scheduling request resource type; determiningthat a change from the first scheduling request resource type to thesecond scheduling request resource type is desirable; and upondetermining that a change in scheduling request resource type isdesirable, transmitting scheduling requests on the further assignedresource associated with the second scheduling request resource type.28. A method according to claim 27 wherein at least one of the assignedscheduling request resources is a shared resource assigned to aplurality of UEs of the wireless system and at least one of the assignedscheduling request resources is a dedicated resource assigned only tothe UE.
 29. A method according to claim 27 wherein determining that achange of scheduling request resource is desirable comprises detecting achange in activity of the UE based on one or more of: a current dataactivity status or a data activity level relating to the UE; an activityrelating to one or more applications resident on the UE; an activityrelating to services or logical channels associated with the UE; adiscontinuous reception timer DRX state or sub-state; a change inpattern relating to a DRX; a determination of whether one or more timerscontrolling DRX behaviour are running or have expired; a determinationor measurement of pathloss between the eNB and the UE; a determinationor measurement of a downlink carrier to interference C/I or downlinkcarrier to interference-plus-noise C/N+I; a determination or measurementof a uplink carrier to interference C/I or uplink carrier tointerference-plus-noise C/N+I; an uplink data rate for the UE; an uplinkmodulation and coding scheme for the UE; a ratio of maximum UE transmitpower to a current UE transmit power.
 30. A method according to claim 29wherein determining that a change of scheduling request resource isdesirable comprises receiving an explicit signal from an eNB specifyingwhich assigned scheduling request resource to use.
 31. A methodaccording to claim 1 wherein SC-FDMA is used by the UE for uplinkcommunication signals sent by the UE.
 32. A method according to claim 1,wherein a modulation scheme other than SC-FDMA is used for downlinkcommunication signals received by the UE.
 33. A user equipment UE for asingle carrier frequency division multiple access SC-FDMA system,comprising: one or more processors configured to: receive an assignmentof a recurring scheduling request resource in the wireless systemcomprising a plurality of subcarriers, wherein the recurring schedulingrequest resource is assigned to a plurality of UEs; encode a user ID;and transmit an SC-FDMA uplink control channel signal comprising theencoded user ID on the plurality of subcarriers of the assignedscheduling request resource.
 34. The UE of claim 33, wherein theassignment is received from a broadcast transmission or commonsignalling message transmitted by an eNB of the wireless system.
 35. TheUE of claim 33, wherein the assignment is received from a dedicatedtransmission to the UE by an eNB of the wireless system.
 36. The UE ofclaim 33, wherein the user ID is related to a Cell Radio NetworkTemporary Identifier C-RNTI.
 37. The UE of claim 33, wherein the SC-FDMAuplink control channel signal comprises a Physical Uplink ControlChannel PUCCH format 2 or format 3 signal.
 38. The UE of claim 33,wherein the user ID is encoded with a non-user-specific bit scramblingsequence.
 39. The UE of claim 33, wherein the scheduling requestresource comprises a plurality of constituent scheduling requestresources, and wherein the one or more processors are further configuredto: select a constituent resource from the plurality of constituentresources; and transmit the SC-FDMA uplink control channel signal on theselected constituent resource.
 40. The UE of claim 33, wherein theassigned scheduling request resource is within a PUCCH frequency regionor a PUSCH frequency region of an uplink system bandwidth of thewireless system.
 41. The UE of claim 33, wherein the one or moreprocessors are further configured to calculate and append a cyclicredundancy check code CRC to the transmission.
 42. The UE of claim 33,wherein said UE comprises a plurality of antennas and has a plurality ofassociated user IDs, and wherein the one or more processors are furtherconfigured to: associate an antenna with one of the user IDs; encode theuser ID associated with the antenna; and use at least the antennaassociated with the user ID to transmit the encoded user ID.
 43. The UEof claim 42, wherein the one or more processors are further configuredto select an antenna for transmission by measuring signals transmittedfrom an access node on the plurality of antennas.
 44. A non-transitorycomputer-readable medium storing instructions to cause a processor toperform operations comprising: receiving an assignment of a recurringscheduling request resource in the wireless system comprising aplurality of subcarriers, wherein the recurring scheduling requestresource is assigned to a plurality of UEs; encoding a user ID; andtransmitting an SC-FDMA uplink control channel signal comprising theencoded user ID on the plurality of subcarriers of the assignedscheduling request resource.
 45. A method implemented in a userequipment UE for a wireless telecommunications system comprising:receiving an assignment of a recurring scheduling request resourcecomprising a plurality of subcarriers, wherein the recurring schedulingrequest resource is assigned to a plurality of UEs; determining a needto transmit on scheduled uplink resources; encoding a user ID togenerate encoded bits; modulating the encoded bits to produce modulatedsymbols; spreading the modulated symbols; mapping each of the spreadmodulated symbols to the plurality of subcarriers; and upon determininga need to transmit on scheduled uplink resources, transmitting anSC-FDMA uplink control channel signal comprising the plurality ofsubcarriers of the assigned scheduling request resource.